AP

KANSAS CITY, Mo. (AP) — Patrick Mahomes was flushed from the pocket and scrambled all the way to his left, only to realize that just about everybody wearing a Chiefs helmet was on the opposite side of the field.

It was a rookie mistake by the second-year pro, one he turned into more early season magic.

Mahomes quickly reversed field against the pursuing San Francisco defense, ran all the way to the other side and threw a dart to Chris Conley in the back of the end zone. It was one of three TD passes he threw in a 38-27 victory over the 49ers on Sunday — and easily the most impressive .

"That," Chiefs coach Andy Reid acknowledged with a smile, "was a good one."

Mahomes finished with 314 yards passing in his first regular-season start at Arrowhead Stadium, and his touchdown throws to Conley, Demetrius Harris and Sammy Watkins gave him 13 this season without an interception. That total broke the NFL record of 12 for the first three weeks of a season, set by Peyton Manning during the 2013 campaign.

More importantly, all those touchdown tosses have the Chiefs 3-0. They are the third team to score at least 38 points in each of the first three games, joining 2007 New England and the 1967 Baltimore Colts.

"We've got a bunch of weapons," said Chiefs running back Kareem Hunt, who added his first two touchdown runs this season, "and Pat is just a competitor. I knew that from the day we met, when we got drafted together. We said one day we were going to take over the Chiefs Kingdom."

The Chiefs have clearly found their long-term answer at quarterback.

The 49ers? They have a whole lot of questions now.

Jimmy Garoppolo left late in the fourth quarter after his left knee buckled during a scramble to the sideline. He was crushed on his throwing shoulder by the Chiefs' Steven Nelson, but the damage was already done, and the 49ers' franchise quarterback was carted off to the locker room.

"We fear an ACL," 49ers coach Kyle Shanahan said. "We'll find out for sure tomorrow."

The 49ers (1-2) trailed 35-7 late in the first half before rallying behind Garoppolo, who threw for 251 yards and two touchdowns. Matt Breida added 90 yards rushing and Alfred Morris scored on the ground as San Francisco clawed to within 35-24 late in the third quarter.

It was still 38-24 when the 49ers produced a grinding, 17-play drive that wiped out more than half the fourth quarter. But it ended in a strange sequence that began with Garoppolo taking the shot from Nelson along the sideline, rather than stepping out of bounds and avoiding the hit.

"I think that was his fault," said Chiefs linebacker Justin Houston, who was trailing the play. "I pray he's not hurt, it's nothing serious, but as a quarterback you should step out of bounds. It's only an inch. An inch wouldn't have made a difference. You got the yardage. You need to be smart."

C.J. Beathard came in on third-and-goal and threw what appeared to be a touchdown pass to George Kittle, but it was wiped out by offensive pass interference with 5:17 left in the game.

Rather than go for it on fourth down at the Kansas City 25, Shanahan elected to kick a field goal — keeping it a two-possession game. Then the 49ers kicked it deep rather than try an onside kick, and the Chiefs picked up a first down by penalty before Hunt churned for two more and put the game away.

"That's our time in the game," Reid said. "You take a lot of pride in it. They're going backward and we're going forward and it's all good."

MORE ON GAROPPOLO

Shanahan acknowledged a quarterback move is likely, though Beathard is line to start next week in Los Angeles. The 49ers' only other QB is Nick Mullins, a member of the practice squad. "I just talked to (Garoppolo) in the training room," Beathard said. "I told him I'll be praying for him and I love him and he just told me to lead these guys."

FOSTER'S FRUSTRATION

49ers LB Reuben Foster had a rough return from a two-game suspension for violating the league's personal conduct and substance abuse policy. Foster was hit with a personal foul for hitting Mahomes as the QB was sliding in the first half, Kelce beat him in pass defense, and the young linebacker left early in the fourth quarter when he was shaken up on a tackle.

INJURIES

49ers: The defensive backfield was in tatters by the fourth quarter. CB Richard Sherman left with a calf injury, FS Adrian Colbert hurt his ankle and backup CB Tarvarius Moore left with a wrist injury. SS Jaquiski Taylor was already inactive with a shoulder injury.

Chiefs: LB Dee Ford left with a groin injury in the fourth quarter. He will have an MRI exam Monday ... Conley briefly left with a right ankle injury, though he returned to make his TD catch. ... SS Eric Berry (heel) remained inactive for the third straight week.

UP NEXT

49ers: Play the Chargers in Los Angeles next Sunday.

Chiefs: Visit the AFC West-rival Broncos next Monday night.

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