HOUSTON (AP) The Kansas City Chiefs got another big game from Alex Smith and a little help on special teams to remain undefeated Sunday night.

Smith threw for 324 yards and three touchdowns and Tyreek Hill added a punt return score in the fourth quarter to lead the Chiefs to a 42-34 victory over the Houston Texans in a game where J.J. Watt broke his left leg.

Deshaun Watson's 48-yard touchdown pass got the Texans within six early in the fourth quarter before Smith extended the lead for Kansas City (5-0) to 32-20 on a 10-yard pass to De'Anthony Thomas with about nine minutes left.

''Once they made it a one-score game, I knew the onus was back on us to go answer,'' Smith said. ''If you keep answering them, it kind of becomes demoralizing when you make it a two-score game again.''

It's the second 300-yard passing game for Smith this season and gives him 11 touchdown throws.

Hill padded the lead when he returned a punt 82 yards for a touchdown.

Watson threw for 261 yards and five touchdowns, but the Texans (2-3) failed to recreate the magic they found last week when they scored a franchise-record 57 points in a victory over Tennessee.

''I think every game is a learning experience for him,'' coach Bill O'Brien said. ''I really think he's an excellent young quarterback and I thought he kept competing right to the end. He's a great kid, he's a lot of fun to coach and he's obviously got a great future.''

Watt, the three-time Defensive Player of the Year, was injured in the first quarter and the team announced that he sustained a tibial plateau fracture, but didn't provide any details on how long he'll be out. The defensive end returned this season after missing the final 13 games last year after his second back surgery.

''I feel terrible for the guy,'' O'Brien said. ''But ... just knowing him and knowing the type of guy that he is, he's an amazing human being. And he will work extremely hard to be back to play for this football team. I know that.''

The Texans cut their deficit when Watson threw a 9-yard touchdown pass to Fuller in the third quarter. But the 2-point conversion failed, leaving them down 23-13.

Kansas City's Charcandrick West caught two touchdown passes and Travis Kelce had eight receptions for 98 yards in the first half, but didn't return after halftime and the team said he was being evaluated for a concussion.

The Chiefs were up by six when Smith found West on an 8-yard touchdown pass to make it 13-0 in the second quarter. Houston rookie D'Onta Foreman fumbled two plays later to give Kansas City the ball right back and the Chiefs tacked on a field goal.

Foreman stepped out of one tackle before plowing over Marcus Peters as he tried to tackle him before two other Chiefs finally brought him down after a 25-yard gain that got Houston to the 10 on the Texans' next drive. The Texans cut it to 16-7 when Watson found DeAndre Hopkins in the back of the end zone for a 6-yard touchdown pass with about two minutes left in the first half.

''We played a good team,'' Hopkins said. ''A team like that, you can't make many mistakes because they're a good team. They're undefeated for a reason.''

Smith then connected with West again, this time on a 4-yard TD pass to put the Chiefs up 23-7 at halftime.

The Chiefs led 3-0 early after a 35-yard field goal by Harrison Butker on their first drive. Watt was injured on the play before the field goal and fell to the ground while being blocked. Watt remained on his hands and knees for a couple of minutes while trainers checked on him.

They flipped him onto his back and were looking at his left leg. He was then helped to his feet and looked to be in a lot of pain and didn't appear to be able to put any weight on the leg as he was helped off the field by two Texans officials. He remained on the sideline under a tent for a few minutes before being taken to the locker room on a cart and then taken by ambulance to the hospital.

Butker added another field goal early in the second quarter to make it 6-0.

Kansas City rookie Kareem Hunt had 29 carries for 107 yards to give him four 100-yard rushing games this season.

''Hunt just continues to stay strong in the fourth quarter with his endurance. He's got ball-carrying endurance,'' Reid said. ''I don't know, for a big guy, he can skedaddle and we really needed him there.''

Hopkins had four receptions for 52 yards with three touchdowns after catching two late scoring passes when the game was out of reach.

INJURY REPORT

Chiefs' safety Steven Terrell suffered a concussion on the opening kickoff. ... Houston linebacker Whitney Mercilus injured his chest in the first quarter and didn't return. O'Brien said he is concerned about the injury, but didn't provide any details on it. ... Houston safety Corey Moore suffered a concussion. ... Reid said that he thinks receiver Chris Conley has a ruptured Achilles tendon.

UP NEXT

Chiefs: Host Steelers next Sunday.

Texans: Host Cleveland next Sunday.

---

For more AP NFL coverage: http://pro32.ap.org and http://twitter.com/AP-NFL

Copyright 2017 by STATS. Any commercial use or distribution without the express written consent of STATS is strictly prohibited.