A rematch between the reigning conference champions ended like the Super Bowl eight months ago: with a victory for the Kansas City Chiefs.

The Chiefs defeated the San Francisco 49ers 28-18 and improved to 6-0 for the first time in Patrick Mahomes' decorated career.

Brock Purdy and his injury-riddled receiving group fell to 3-4, overwhelmed by the Chiefs' blitz attack plan.

Each team got off to a chaotic start on a dangerous day for the passing game, with Purdy and quarterback Patrick Mahomes combining for zero passing touchdowns and five interceptions.

Mahomes rushed for the game-winning touchdown, while Purdy scored two points of his own, including a 1-yard touchdown with 1:08 to play that might have opened up a final chance for a comeback had the 2-point conversion attempt worked.

However, that was not the case, and San Francisco will reflect on this loss while also determining the severity of a veteran player's recent injury.

Brandon Aiyuk's right knee collapsed on the impact of a tackle on a 15-yard catch in the final minute of the first half. He grimaced as he was carted off and was soon ruled out by Deebo Samuel Sr. (illness), Christian McCaffrey (calf/injured reserve) and Jauan Jennings (hip) as they were unavailable.

After the game, 49ers head coach Kyle Shanahan said the team feared Aiyuk would suffer an ACL injury.

Purdy had bright spots with his cast of second- and third-string receivers, but the Chiefs' teeming front seven significantly disrupted San Francisco's offensive rhythm, limiting the Niners to 2 of 11 on third down.

Three plays after Purdy nailed Jacob Cowing 41 yards downfield in the fourth quarter, Chiefs edge rusher George Karlaftis hit Purdy's arm and contributed to an end zone interception with 9:34 to play.

The Chiefs squandered the clock and the 49ers' chances with a long scoring drive that sealed their victory – and preserved their unblemished record.

A day full of takeaways favored the Chiefs

After the 49ers started the game with a three-and-out, San Francisco fended off a fake punt attempt and stopped the Chiefs one yard short of fourth-and-2. But the Niners' momentum was short-lived as Purdy dropped back moments later and Karlaftis closed in and Justin Reid, 11 yards further down the field, snatched the pass intended for George Kittle.

Four more total interceptions would follow.

Mahomes made his first appearance on the ensuing series when defensive tackle Kalia Davis tipped over and then picked off his pass on 2nd-and-15.

The 49ers capitalized on the turnover with their first points of the day, a 55-yard field goal, thanks in part to a pass interference flag that Reid drew.

But with the Niners failing to find the end zone in the first half, the Chiefs ran tricks and Xavier Worthy's end-arounds, Mahomes' defensive diagnostics and Mahomes' physics so unusual that Tom Brady wondered on the broadcast whether Bill Belichick at home “on the field” was “tearing my hair out” and watching Mahomes “break every quarterback rule I learned.”

No matter: Mahomes did enough to get the Chiefs into the red zone five times, with running back Kareem Hunt rushing for the Chiefs' first two touchdowns on each occasion.

Tight coverage limited Purdy's targets while unblocked blitzers overran his mechanics and neutralized third-down attempts after another.

The 49ers' bright spot in the first half was receiver Ricky Pearsall catching a 6-yard pass with 1:32 to play in the first half, less than two months after the rookie was shot in a suspected armed robbery. It was Pearsall's regular season debut.

Whether this directly juiced the 49ers or the timing was fortuitous, Purdy completed his next three passes in a row — a 41-yarder down the left sideline to Kittle, a short pass to Jordan Mason and then a 15-yarder to Aiyuk.

But Aiyuk's knee gave way during the play, it was his last action of the day. The 49ers' field goal before halftime cut their deficit to one point. But they would never catch the Chiefs.

The 49ers opened the second half with a determination that could not guarantee their luck on the day. When Worthy, the Chiefs' rookie receiver in the first round, slipped on a corner route after Mahomes released his pass, 49ers defensive back Deommodore Lenoir took advantage of the interception. As the passing game continued to become difficult, Purdy gained 9 yards on third down and then the quarterback keeper on fourth-and-1.

That would have been San Francisco's first touchdown, a Purdy sneak with three tight ends and two pulling right guards with 10:29 left in the third.

“That was pretty sick,” Brady enthused about the play’s design.

An apparent miscommunication between Purdy and a flatter-than-the-throw Ronnie Bell gave the Chiefs their second interception. The Chiefs marched down the field with a mix of running and passing plays, with Mahomes scrambling up the left sideline on second and seventh drives, faking pump gaffes and focusing his eyes on perceived dangerous areas enough to somehow reach 33 yards.

On the four-and-goal, Mahomes finished the job. He looked to his left to gauge Kelce's availability, then decided to take matters into his own hands. A game-winning touchdown followed, but Mahomes' fourth score was enough.

Mahomes completed 16 of 27 passes for 154 yards and two interceptions, rushing five times for 39 yards and a touchdown. Hunt led the Chiefs' skill players with 78 yards and two touchdowns on 22 carries.

Purdy completed 17 of 31 passes for 212 yards and three interceptions, carrying eight balls for 27 yards and two touchdowns.

Kittle led all skill players with 92 yards on six catches.