Thirty-one days ago, Roki Sasaki arrived at Dodger Stadium, met with president of baseball operations Andrew Friedman and general manager Brandon Gomes, and was presented a plan that required faith and trust.

It had been eight months since Sasaki signed with the Dodgers amid massive expectations, coming over from Japan as a 23-year-old phenom billed as possessing some of the best raw arm talent in the world.

It had been four months since his debut season took a dismal turn, landing on the injured list with a shoulder impingement following an opening month marred by poor performance and diminished stuff.

Less than two weeks earlier, Dodgers manager Dave Roberts had all but written Sasaki off as a potential factor in the team’s postseason plans, after the pitcher had continued to struggle in a minor-league rehab stint.

But then, two days before his meeting with club brass, Sasaki had finally shown some signs of life, striking out eight batters during an auspicious start with triple-A Oklahoma City in which his fastball once again touched 100 mph and his trademark splitter was almost unhittable.

So, as the team began looking ahead to October, Friedman and Gomes sat Sasaki down alongside his interpreter, and presented what has proven to be a season-altering idea — for him, and his new team.

The Dodgers knew Sasaki was unlikely to feature as a starting pitcher in October, given their healthy and dominant rotation. But they saw an opportunity to use him as a reliever in the playoffs.

Only, however, if he were also open to it.

“We were just honest with him, that as things stood, the only real pathway — short of multiple injuries — was in the bullpen,” Friedman said. “But we wanted his full buy-in.”

Long-term, they promised him, he would still be a starter. In their view, he was assured, the team still saw him as a potential future ace.

But for now, they asked if he’d be open to making a temporary move to the bullpen; to taking on a relief role that they knew to him was completely foreign.

“We don’t want an answer right now,” Friedman told Sasaki. “We want you to take time and think through it.”

“We would not want to push this,” he added, “unless you’re totally on board.”

All year, the Dodgers had tried to build trust with their newest Japanese star. Now, they waited for an answer, as Sasaki went home and mulled things over alongside his agent.

As he later told the Japanese magazine Shukan Bunshun, he was initially “very hesitant” to such a switch. There was a time in middle school he’d been a closer, but during his ascent from high school to the pros, starting was all he’d ever known.

Several things, however, tipped the scales in his mind. He craved a chance to pitch in a postseason environment. He sensed an opportunity to boost a team in desperate need of relief depth. And, having finally found a comfort level with his club after a trying rookie season, he’d regained the confidence he was missing at the start of the campaign.

Thus, before the end of that day on Sept. 11, Sasaki gave the Dodgers his answer. He was in.

“Because they will let me try to start again next season,” he said, “it was a relatively easy decision to make.”

Thirty-one days — and 5 ⅓ scoreless, invaluable innings of postseason relief work from Sasaki — later, it was a moment that might have helped save the Dodgers season, and launch the rest of his MLB career.

From the day Sasaki signed with the Dodgers in January, his agent, Joel Wolfe of Wasserman Media Group, was quick to remind reporters that his young client was “not a finished product by any stretch.”

Turned out, he didn’t come to the majors completely healthy either.

During his final couple seasons in Japan, Sasaki’s fastball velocity had dipped while battling shoulder and oblique injuries. He couldn’t explode down the mound with his high leg kick the way he once did. He wasn’t consistently hitting 100 mph on the radar gun or dotting the strike zone with his typically pristine command.

His delivery, evaluators noticed, had begun to suffer. A throw built on generating torque from his legs to his hips and on through his shoulder and lengthy right arm, instead started to look inefficient and uncomfortable.

“I think a lot of it just came from his body changing the way he was throwing,” said Dodgers director of pitching Rob Hill, who had closely admired Sasaki during his Japanese career. “Due to kind of throwing hurt for probably a couple years.”

Once he joined the Dodgers this year, Sasaki hit rock bottom. His oblique no longer bothered him. But his shoulder remained sore and stiff. His fastball eclipsed triple-digits a couple times in his adrenaline-fueled MLB debut in Tokyo in March, but quickly plummeted upon returning stateside, averaging just 95.7 mph (and dipping all the way to 93 mph and below) over his seven subsequent starts.

When coupled with erratic control (he walked 22 batters in 34 ⅓ innings), and a flat pitch shape that made his four-seamer relatively easy to hit (lacking the vertical “ride” required to fool MLB batters long accustomed to combating big velo), opponents began teeing off. By the time Sasaki finally went on the injured list with a shoulder impingement in early May, he had a 4.72 ERA and some of the worst underlying metrics in the majors.

“We go back to the drawing board every week with him,” pitching coach Mark Prior said at the time. “We’re just trying to support him with everything we can.”

At first, Sasaki seemed slow to embrace it. Not only was there a language barrier between him and his new club, but the rookie also built walls around his personality. Quiet by nature and “very particular” in temperament, as Wolfe described him this winter, Sasaki tried to keep a steadfast routine. He didn’t want to alter his pitch mix. He searched for his own ways to iron out his mechanics.

But all he found instead was frustration, leaving him looking lost in his new surroundings — and sinking even lower when lingering shoulder pain in early June further delayed his recovery timeline and required a cortisone injection.

“I think like any new player that you acquire, it takes a little while to build up trust,” Friedman said. “We knew that he was a guy that was accustomed to doing things a certain way, and we were going to embrace that, [while] at the same time forging a relationship and building trust and getting to a place where we could partner together.”

It would take time for the two sides to get there.

As Sasaki tells it, the turning point in his season happened three days before that meeting with Friedman and Gomes; on the eve of the rehab start that triggered their suggestion to move to the bullpen.

Sitting in his Oklahoma City hotel room that night, Sasaki pulled up old video of his high school days and studied a delivery that, even then, enthralled evaluators around the sport.

He was looking to the past to find answers in the present.

“I felt,” he later recounted to Shukan Bunshun, “like I was about to notice something.”

So, he kept watching.

In the three months before then, Sasaki and the Dodgers had finally started making progress.

After his initial injury setback, he formed a connection with head team physician Dr. Neal ElAttrache — the renowned orthopedic surgeon who not only laid out a plan for Sasaki’s recovery, but more important allayed fears of continued problems through what Sasaki described as a “very educational” process.

As Sasaki’s shoulder calmed down, he took strides in the weight room as well, working with Dodgers strength coach Travis Smith to add explosiveness and strength (especially in his lower body) to his once-scrawny 6-foot-2 frame.

“I feel better about being able to throw harder,” Sasaki said in August, as he headed out on a long-awaited rehab assignment, “especially because I’m completely pain free.”

Sasaki’s first four starts in triple-A were still a mixed bag. His velocity gradually improved, but remained mostly struck in the mid-90s. He tinkered with new pitches, including a cutter and sinker, but still couldn’t execute his trademark splitter the way he wanted.

By early September, it was enough for Roberts to cast doubt on Sasaki’s return, saying bluntly that “the performance, the stuff hasn’t been there.”

“Roki has gone through a lot this year, and he still has a ton of talent,” Roberts added. “We just want to see more.”

One week later, they finally would.

During a trip to the team’s Arizona training complex in the following days, Sasaki met with Hill and his pitching development staff, spending several hours reviewing video of his throw.

As Hill described it last month, they weren’t so much “solving this master plan” with Sasaki as they were “helping him actualize the things” he was trying to do in his delivery. They suggested tweaks to Sasaki’s lower-half mechanics. They emphasized the way he fired his hips as he launched down the mound.

Sasaki listened, and agreed on what they identified as the root causes of his struggles. One day that week, he even tested some of the changes in what was one of his hardest bullpen sessions all year.

“The day of that bullpen, it was like, ‘Holy s—,’” Friedman recalled thinking. “Things are in a really good spot.”

Sasaki, however, hadn’t convinced himself of that yet. While Hill’s evaluation “matched up with what I thought wasn’t going well,” he said in Japanese last week, “the approach [to fixing it] was a different story.”

That’s why, when Sasaki returned to Oklahoma for his next start days later, he went back over more video, and waited for a revelation.

It was then, he said, “I noticed something about the use of my lower body.”

Like a high jumper with a disjointed sequence while lifting off the ground, Sasaki felt he was still losing too much power between his leg kick and release — drawing a contrast to what he saw in his old high school motion.

Dodgers first baseman Freddie Freeman gives the ball to pitcher Roki Sasaki after he closed out the ninth inning to preserve the win against the Philadelphia Phillies in Game 2 of the NLDS.

(Robert Gauthier / Los Angeles Times)

So, for the rest of that night, he did dry throws in his room in search of a specific feel. All those months of work with the Dodgers’ medical team, training staff and pitching coaches suddenly tied together. For the first time all year, he felt like his old self again.

The next evening, he took the mound and hit 100 mph six times. He coupled it with extra life and movement on his knuckle-balling splitter. And he showed enough for Dodgers brass to call him back to Dodger Stadium and inquire about the bullpen.

“We think you can be really good in this role,” Friedman told him. “This is the potential pathway to help us in October.”

Of course, no one saw the level of dominance that was on the horizon. After completing his minor-league stint with two scoreless relief appearances, Sasaki rejoined the Dodgers for the final week of the regular season, showcased his improved stuff with two more scoreless innings of relief, then made a rapid ascent to de facto postseason closer — producing zero after zero when other relievers faltered around him.

He recorded the final outs of the team’s wild-card round sweep of the Cincinnati Reds. He picked up back-to-back saves in Games 1 and 2 of the National League Division Series against the Philadelphia Phillies, becoming the first pitcher to record his first two career saves in the playoffs. He spun three perfect innings in the club’s Game 4 clincher on Thursday.

“One of the great all-time appearances out of the ‘pen that I can remember,” Roberts called it.

“Since coming back, coming in from the bullpen,” added teammate Tyler Glasnow, “he’s honestly one of the best pitchers I’ve ever seen.”

It has all come with a renewed level of confidence too. After that Game 4 masterclass (in which he was so locked in he didn’t even remove his glove in the dugout between innings), Sasaki said he has felt no nerves in the playoffs, nor any hesitancy about attacking the strike zone.

All those frustrations from early in the season have evaporated. His process of building trust within the organization while rediscovering the best version of himself on the mound has come suddenly, electrifyingly complete.

“The stuff being there lines up with what our expectations were,” Friedman said. “But the poise and composure, you don’t know until someone’s out there. And I would say he has more than answered the bell.”