Alex Smith threw for four touchdown passes, rookie running back Kareem Hunt scored three times after fumbling away the first carry of his pro career, and the Kansas City Chiefs spoiled the Patriots’ Super Bowl celebration with a stunning 42-27 upset of New England in the NFL season opener Thursday night.

The Patriots had been 81-0 at Gillette Stadium when leading at the half in the regular season — 95-1 counting the postseason — before the Chiefs came back from a 17-14 halftime deficit. New England also was 105-2 when leading after three quarters as it entered the fourth up 27-21.

The 42 points are the most scored against the Patriots since coach Bill Belichick took over in 2000, a span of 307 games, including playoffs.

Smith was 28 of 35 for 368 yards and hit Tyreek Hill and Hunt with touchdown bombs of 75 and 78 yards, respectively.

Hunt, who became the starter when Spencer Ware was lost for the season during the preseason, ran for seven yards but coughed the ball up on his first carry. But he went on to run for 148 yards and one touchdown on 17 carries and catch five passes for 98 yards and two touchdowns.

Hunt’s late 58-yard run preceded a 21-yard touchdown run by Charcandrick West with four minutes left as the Chiefs ran up 537 yards of offense and scored on drives in 90, 92 and 90 yards.

The Patriots, who lost Julian Edelman for the year during the preseason, saw linebacker Dont’a Hightower leave the game in the third quarter with a right leg injury and wide receiver Danny Amendola leave in the fourth to enter concussion protocol.

New England’s Tom Brady was 16 of 36 for 267 yards in the loss, six of the completions to Amendola, who had his eighth career 100-yard game.

Mike Gillislee, making his Patriots debut, scored all three New England touchdowns. He and Hunt became the first players with three rushing touchdowns in their first game with a team since Marshall Faulk accomplished the feat for the Indianapolis Colts in 1994.

Smith became the first Chiefs quarterback with two touchdown passes of at least 75 yards in a game since Len Dawson did it — to the Boston Patriots in 1968. He is the second quarterback to throw for at least 300 yards and at least four touchdowns with no interceptions against a Belichick defense.

Hunt became the third player ever — the first since Faulk in 1994 — with 150 scrimmage yards and three scores in his debut.

Hill caught seven passes for 133 yards and a touchdown.

Gillislee scored his first touchdown twice. He went in from 2 yards out but offsetting penalties brought it back, and he scored again two plays later to cap the opening drive.

Hunt then fumbled away his first NFL carry after a 7-yard gain. Brady hit Gronkowski with a 20-yard touchdown that was also called back — this one on review — and Gillislee was stopped on a fourth and less than a yard at the 10.

Smith then went 7 of 8 through the air to bring his team 90 yards for a 7-7 tie as he drilled a 7-yard touchdown pass to Demetrius Harris.

The Kansas City defense made a big third-down stop on James White and the Patriots settled for Stephen Gostkowski’s 25-yard field goal to take a 10-7 lead. Gillislee scored his second touchdown on New England’s next possession to make it 17-7.

The Chiefs started a drive at their own 8 and were sent back to the 4 on a penalty, but Smith brought them down the field again. A 20-yard pass interference penalty against Malcolm Butler in the end zone put the ball at the New England 1.

After a 2-yard loss, it was Smith to Hunt for the touchdown with 13 seconds left and it was 17-14 at the half.