LAS VEGAS - The Kansas City Chiefs stayed undefeated and handed the Las Vegas Raiders their first loss of the season with a wild, back-and-forth 30-27 victory in Las Vegas on Sunday. For most of the game, the Las Vegas defense held the Chiefs in check thanks to constant pressure on Patrick Mahomes. But late in the third quarter, Kenneth Walker III broke free for a 77-yard run, setting up Tyquan Thornton's second touchdown catch of the day and giving the Chiefs a 17-13 lead. The Raiders re-took the lead with two field goal drives before Thornton delivered the game's biggest play. On a third-and-5 from their own 40, with the Raiders sending an all-out blitz, Thornton got behind his defender and Mahomes lofted a high-arching pass that fell into his hands. Thornton was tackled at the 5, setting up Walker's go-ahead touchdown run, but suffered a gruesome ankle injury as he was brought down. On the ensuing kickoff, Jeffrey Bassa punched the ball free from return man Dareke Young and the Chiefs fell on the fumble. On the next play, Walker ran for a 22-yard touchdown, stretching the Chiefs' lead to 30-19. Cousins led the Raiders on a scoring drive to cut the lead to three and Las Vegas got the ball back after forcing a three-and-out, foiled in part by a bad snap on third-and-8. However, Matt Araiza delivered a 52-yard punt that was downed at the Las Vegas 1, forcing a lengthy drive the Raiders couldn't complete. Cousins drove the Raiders to midfield with 10 seconds left. Running one last play to try to move into closer field-goal range, Cousins' arm was hit by George Karlaftis as he threw and his pass was intercepted by Xavier Nwankpa. One of the game's pivotal moments came early in the third quarter. Las Vegas's Matt Gay made a 41-yard field goal on the opening possession of the second half, but the Chiefs were flagged for an illegal formation. Raiders coach Klint Kubiak chose to take the penalty, setting up a fourth-and-2 but taking the points off the board. Kirk Cousins' pass fell incomplete Box score | Week 4 live blog | Game discussion This game was back and forth throughout. How much separation is there between these two teams? The Raiders pushed the Chiefs to the end, no doubt, but I'd still expect Kansas City to be about a touchdown favorite when the rematch comes back to K.C. in Week 18. To me, that signifies a decent statistical gap remains between the teams. The fact we're having this conversation just four weeks into the season, though, is a huge compliment to Kubiak, who has immediately elevated Las Vegas to a legitimate AFC playoff contender. - Jesse Newell, Chiefs beat writer In terms of on-field talent, not much. The Raiders showed they can hang around with one of the AFC's best teams. That's an incredible feat for a squad that won just three games a year ago, and a sign of how much they've improved under this new regime. The difference on Sunday was their end-game execution, both coaching and on-field play. The Raiders' staff was inconsistent with its decisions, as Kubiak opted to be conservative and kick a field goal instead of going for it on a fourth-and-short, one quarter after he'd taken three points off the board and opted to go for a fourth-and-2. After Kubiak's conservative decision, defensive coordinator Rob Leonard was aggressive on the game's key play, sending an all-out blitz on third down, which allowed Mahomes to hit Thornton on an explosive play to set up Kansas City's go-ahead touchdown. Execution issues then hit the Raiders' special teams. Las Vegas made a valiant effort in the final two minutes, but ultimately misplayed its final snap. Despite the fact the clock was stopped after a spike, they had a disjointed operation and drew an illegal shift penalty, which was ultimately declined due to the game-ending interception. The Raiders proved they're up there with anyone talent-wise. They still need to learn how to win against the best, however. - Sam Warren, Raiders beat writer How alarming was the Chiefs' inability to protect Mahomes? Pass protection remains the biggest concern for the Chiefs as they look to rejoin the NFL's elite. We highlighted it last week when Mahomes was pummeled repeatedly during the second half against the Miami Dolphins. He endured the same for most of Sunday's game. The Chiefs struggled to stop the Raiders' pass rush on obvious passing downs. We should note here: The Chiefs getting to 4-0 is a major credit to coach Andy Reid and offensive coordinator Eric Bieniemy. The team has leaned heavily on play-action and gone frequently to the quick passing game to mask an obvious issue. Kansas City has to hope that starting left tackle Josh Simmons heals soon from the back ailment that has sidelined him for the first four games, and perhaps a bye week will help. A new concern, though? The Chiefs benched left guard Kingsley Suamataia on Sunday in favor of veteran Mike Caliendo. Will that be a long-term thing? Suddenly, K.C. seems to have question marks everywhere besides its anchors at center (Creed Humphrey) and right guard (Trey Smith). - Newell Maxx Crosby was frequently on and around Patrick Mahomes - would this Raiders defense have held up in a game where they had zero takeaways if Crosby was in Baltimore instead? Definitely not. Mahomes looked like himself when he had time to throw against the Raiders' defense. Throws of 41 yards to Xavier Worthy and 42 yards to Thornton that set up Kansas City's first-half scores were with clean pockets. But because of Crosby's pursuit, those clean pockets were few and far between, leaving Mahomes looking less than MVP-caliber. While he had just half a sack, Crosby posted five hits on Mahomes. He became just the fifth player in the NFL this season to reach the total. Those blows took a toll, as Mahomes missed on a few throws when pressured. Some of those came from other Raiders defenders, but attention on Crosby helped open rush lanes. The Crosby trade going through would have given general manager John Spytek more room to operate financially. But without the star edge rusher's presence, the Raiders' defense wouldn't have limited Mahomes to nearly the extent it did. - Warren If Rashee Rice and Tyquan Thornton potentially miss time, how does that change the Chiefs' offense? Receiver depth was one of the team's biggest concerns heading into the season, and it now likely pushes back to the top of the wish list with the trade deadline looming. Thornton - who had five catches for 111 yards and two touchdowns Sunday before the injury - could be lost for the season, judging by how severe it initially appeared. Rice returned to the sideline Sunday for a while following his non-contact hamstring issue, which could suggest an earlier return timeline (perhaps even after next week's bye). In any case, the Chiefs have long been rumored to reunite with past star Tyreek Hill this offseason, and Sunday's events could add urgency to figuring something out once Hill is cleared to return from rehabbing his own knee injury. For the short term, if Rice remains out, expect the Chiefs to lean more on second-year player Jalen Royals, who possesses a similar yards-after-catch skill set to Rice. Fifth-round rookie Cyrus Allen - a man-coverage-beating specialist - should also see his offensive snaps increase with Thornton out. - Newell