Walker’s 76-yard run in the third quarter was clocked at 21.21 mph, and his short touchdowns bookended the fourth quarter that broke the game open.

The score moved Kansas City to 4-0 and left Patrick Mahomes with a 6-0 record at Allegiant Stadium against Las Vegas. Head coach Andy Reid went to 7-1 at the venue, the most wins by any coach there.

A rookie record now belongs to Walker

Four games into his Chiefs career, Walker has rushed for 537 yards, leading the NFL by more than 100. The total surpasses the 534 yards DeMarco Murray put up over the first four weeks of 2014, a record now broken on Murray’s watch, since he is the Chiefs’ running backs coach.

Kansas City won the auction for Walker in free agency last offseason after Seattle let his contract expire. The deal, reported at three years and up to $45 million, was the largest ever handed to a running back in NFL free agency. Walker arrived in Kansas City as the reigning Super Bowl LX MVP.

Read also: Saquon Barkley leaves Eagles vs Rams with hamstring injury in early scare

Mahomes finds a different gear

Mahomes completed 15 of 30 passes for 225 yards and two touchdowns, modest numbers that reflect how much of the offense he has been able to hand off. The Chiefs’ passing game produced the game-swinging play anyway: a 55-yard strike to Tyquan Thornton that set up Walker’s go-ahead two-yard touchdown with 3:21 to play. Thornton, who finished with five catches for 111 yards and two scores, was carted off with a left ankle injury on the reception.

Walker scored again from 22 yards out moments later after the Raiders fumbled the ensuing kickoff, putting Kansas City up 30-19. Rookie safety Xavier Nwankpa sealed it with an interception inside the final 10 seconds.

Cousins kept Las Vegas in it

Kirk Cousins threw for 365 yards and two touchdowns, with tight end Brock Bowers playing through illness for six catches, 86 yards and a score. The Raiders moved the ball through the air but the ground game was shut down to 72 rushing yards at 2.8 yards per carry, and the kickoff fumble after the Walker-Thornton drive proved decisive.

Kansas City is on a bye in Week 5. Walker’s next chance to add to his league-leading rushing total comes when the Chiefs return in Week 6 at home against the Chargers on October 18.

Read also: Benched by Flick, overlooked by Zidane: Kounde points the finger at himself

Read also: Mourinho returns to Roma in the Champions League: the most awkward reunion in European football