And Shanahan figured he was headed for at least mild indigestion Thursday night when Purdy appeared to be doing it again midway through the fourth quarter: With the 49ers only needing to avoid colossal mistakes to beat the Seahawks, Purdy eschewed a safe, wide-open checkdown to tight end George Kittle and targeted Aiyuk, who was 15 yards deeper downfield and encircled by four defenders.

Shanahan’s initial reaction: “I couldn’t believe he was throwing it.” But that feeling was fleeting, disappearing before Purdy’s perfectly placed laser found Aiyuk for a that’s-a-wrap, 28-yard score in the 49ers’ 31-13 win.

“He proved to us while the ball was in the air,” Shanahan said, “it was the right decision.”

In other words, Purdy’s pass hit different than his across-the-field, into-heavy-traffic, 13-yard touchdown pass to Aiyuk in a 34-3 win at Jacksonville on Nov. 12. After that game, Shanahan termed it one of the worst decisions of Purdy’s NFL career and said it took him a while to get over it.

Shanahan’s point: The young QB had gotten lucky. His feelings Thursday: Damn, the 49ers are lucky to have their young QB.

“He made the throw,” Shanahan said. “I wouldn’t have known (it would have worked) until he threw it. Once he threw it, it was obviously there.”

Purdy’s game-sealer was thrown into zone coverage, over safety Quandre Diggs, and it hit Aiyuk in stride before safety Julian Love and cornerback Devon Witherspoon could converge to sandwich him near the goal line.

It was a brilliant throw, but Purdy has delivered other whoa completions into even tighter windows. On Thursday, though, the context surrounding his decision highlighted his blend of gifts and guts.

Early in the third quarter, of course, Purdy had thrown an off-target pass that caromed off running back Christian McCaffrey’s hand, resulting in a 12-yard pick-six by linebacker Jordyn Brooks that pulled the Seahawks within 24-10.

But the mistake — the first pick-six of Purdy’s career — didn’t affect him a quarter later when he ignored the wide-open Kittle and ended the game.

“I’ve got to be smart with the ball, but at the same time I still have to have that aggressive edge to myself and not being afraid to rip stuff in tight windows still,” Purdy said. “That’s where I was in my mindset.”

• Remember when the 49ers were having trouble answering this question: What’s wrong with your supposed-to-be-dominant pass rush?

Suddenly, they are dealing with a far more pleasant issue, struggling to answer these queries: Who got credit for that sack? And that sack? And …

The 49ers had six sacks Thursday, matching their most since Week 5 of last season, and their final three takedowns of quarterback Geno Smith looked vaguely familiar. Each of the sacks were split and each time there were other defenders around the QB pileup who were oh-so-close to earning a half-sack.

Does it feel like the linemen are racing into the backfield?

“It does,” edge rusher Nick Bosa said. “It’s funny, after the game nobody has any idea what their stats are. So that’s a good problem to have.”

The 49ers’ pass rush put an end to a potential problem in the second half when the Seahawks, trailing by 21 points at halftime, had closed to within 24-10 and had 3rd-and-goal at the 7-yard line.

The Seahawks were forced to settle for a field goal after defensive coordinator Steve Wilks blitzed linebackers Fred Warner and Dre Greenlaw, and defensive tackles Javon Hargrave and Arik Armstead split the sack. Bosa was at the bottom of the pile and edge rusher Chase Young leaped on top.

• The 49ers, who had five sacks during their three-game losing streak that preceded Young’s acquisition, have since had 16 sacks in  their three-game winning streak.

“I guess ever since we got Chase Young things kind of flipped, didn’t they?” Warner said.

On Seattle’s next possession, with the 49ers leading 24-13 early in the fourth quarter, the 49ers ended it on 3rd-and-8 from Seattle’s 31-yard line. Again, Wilks blitzed Warner and Greenlaw, and Armstead and Bosa split the sack, with Warner also all over Smith.

The Seahawks’ next possession: Kevin Givens and Bosa split a sack with defensive end Clelin Ferrell inches away from getting on the sack stat sheet.

Bosa was asked if the 49ers might argue about whether credit was properly assigned.

“As long as it’s in the D-line room,” he said, “we’re happy.”

• The 49ers had two easy-to-overlook special-teams plays that could have changed the game’s tenor if they hadn’t been made.

First, rookie cornerback Darrell Luter, a fifth-round pick playing in his second career game, caught returner Dee Eskridge from behind on his 66-yard kickoff return in the first quarter, the third-longest in the NFL this season.

Luter’s tackle prevented a 99-yard runback and forced the Seahawks to settle for a field goal after the 49ers had just completed a game-opening, 71-yard touchdown drive.

Later, in the fourth quarter, with the 49ers leading 24-13 with 11-plus minutes left, Ray-Ray McCloud fumbled on a punt return and linebacker Oren Burks immediately fell on the loose ball at the 49ers’ 36-yard line. Instead of Seattle being in prime position to make it a one-score game, the 49ers put the game away six plays later on Purdy’s TD pass to Aiyuk.

• Running back Christian McCaffrey had scoring runs of 1 and 8 yards. And he deserves an assist for the 49ers’ other rushing TD, wideout Deebo Samuel’s walk-in, 2-yard stroll that capped their game-opening possession.

With McCaffrey lined up behind right tackle Colton McKivitz, Purdy faked a shovel pass to McCaffrey that froze Brooks and Bobby Wagner, leaving them nowhere near Samuel on his run around left end. It also helped that tight end George Kittle, lined up in the left slot, drove safety Jamal Adams into Walla Walla.

• OK, so this has nothing to do with the game, but the most entertaining part of the evening was McCaffrey’s enthusiastic breakdown of the turkey and other Thanksgiving dishes NBC had for the stars of the game at midfield.

McCaffrey is polite and professional in group interviews, but he’s not overly expansive. The trick: Get him to talk about food instead of football.

“That was awesome,” McCaffrey said of NBC’s spread. “It was actually really good turkey, too. I have no idea how they kept all of it — all of the dishes were hot. I was bummed I didn’t get the sweet potatoes with the marshmallows. They had a fork, but we had to pick the turkey leg up. By that time, I was eating the turkey. The turkey was really good. Well cooked. It wasn’t dry at all. And like I said, still hot, which was impressive for being 20 minutes after the game. I don’t know where they kept it, but it was a good turkey.”

McCaffrey attacked an obvious follow-up question: Did they have green-bean casserole?

“No, they had cornbread.” McCaffrey said. “They had sweet potatoes with the marshmallows on top. I forget what you call that. Like I said before, I was kind of bummed I didn’t get to it. The cornbread was good. Still hot. Just like the turkey. I think they had a couple more (dishes) on the other side. But I was on the left side … so I didn’t get to it. But I was happy we got some food after that.”

Reach Eric Branch: ebranch@sfchronicle.com; Twitter: @Eric_Branch