They cheered. They danced. They high-fived.
Thursday was a night of celebration for the New England Patriots.
Until the Kansas City Chiefs came to life.
In a resounding upset of the defending Super Bowl champions, the visiting Chiefs relied on a pristine performance by quarterback Alex Smith and the scorching speed of Tyreek Hill and rookie Kareem Hunt to deliver a 42-27 defeat that left Gillette Stadium as quiet as a library.
The same crowd that toasted the five-time Super Bowl champions, booed NFL Commissioner Roger Goodell, and cheered wildly as the latest banner was unfurled, headed for the exits in stunned disbelief.
The Patriots, favored by nine, had won eight in a row when opening the season at home. Even without star receiver Julian Edelman, done for the year because of a knee injury, they are loaded with talent. They almost went up by two touchdowns in the first six minutes… but there was no writing off the Chiefs, who finished with 537 yards of offense.
The 42 points were the most allowed by the Patriots in the Bill Belichick era — eclipsing the 41 they gave up to the Chiefs in a 2014 loss.
On defense, the Chiefs stymied Tom Brady, who lost for the first time in 10 Thursday night starts.
“We didn’t blink,” Kansas City linebacker Derrick Johnson said. “That’s the best thing we did tonight. We didn’t blink.”
But one of their players did reboot. Hunt coughed up the ball on Kansas City’s first play from scrimmage — a guy who never lost a fumble in four years at Toledo — then put on an amazing show. He finished with 243 yards from scrimmage and three touchdowns, including a catch and carry that covered 78 yards.
“Guys were just letting me know, ‘We got your back,’ to forget about it and come back and make plays,” Hunt said.
Smith was brilliant, completing 28 of 35 passes for 368 yards and four touchdowns. That vastly upstaged Brady, who completed 16 of 36 passes for 267 yards, with no touchdowns or interceptions, and was under heavy pressure, especially after losing security blanket Danny Amendola to a concussion.
“We didn’t make a lot of plays tonight,” Brady said. “We need to be a lot better in a lot of areas. Start with our attitude and our competitiveness.”
The Chiefs took a 21-17 lead just before the midway point of the third quarter, when Hill got behind the defense and turned a long pass into a 75-yard touchdown. He was so far ahead of his pursuers after making the catch, he turned and shot them the peace sign.
“As far as the touchdown, it was Alex and the offensive line, everybody protecting,” Hill said. “Without those guys, I wouldn’t have been able to get down the field … Alex is our leader. We’ve just got to rally behind him, keep supporting him, and he’ll keep taking shots down the field.”
Both teams lost key defensive players. New England linebacker Dont’a Hightower left the game in the third quarter with an apparent knee injury, and All-Pro Kansas City safety Eric Berry was carted off with what looked to be an Achilles injury.
The Patriots led at halftime, 17-14, but the game lopsided at that point.
New England opened with a touchdown drive, then got the ball right back when Hunt fumbled on the visitors’ first play from scrimmage.
The Patriots took possession at the Kansas City 32 and moved all the way to the 10, threatening to take a two-touchdown lead with less than six minutes expired. That’s when the Chiefs made a huge play, stuffing the run for no gain on fourth and one.
Then, Kansas City responded with a 90-yard scoring drive that culminated with a seven-yard touchdown pass from Smith to tight end Demetrius Harris.
Still, the Patriots were knocking on the door throughout the opening quarter, with 20 of their 27 snaps coming in Chiefs territory.
Scoring both of New England’s touchdowns in the first half was running back Mike Gillislee, formerly of Buffalo, a free-agent acquisition in the offseason. He would score a third touchdown to reclaim the lead in the third quarter.
The home crowd was buzzing to celebrate the defending Super Bowl champions, who unveiled their fifth banner during a pregame celebration that included a live performance by the rapper Flo Rida, and with hometown favorite Mark Wahlberg acting as master of ceremonies.
Goodell was in attendance and was booed loudly when he walked onto the visitors’ sideline before the game.
Goodell is public enemy No. 1 among Patriots fans, who feel he unfairly punished Brady for an alleged football-deflating scheme. Although this was shaping up to be Goodell’s first trip back to Gillette since Brady served his four-game suspension, the commissioner actually attended an exhibition game here in August.
A barely audible Belichick summed up the night: “Bad defense. Bad coaching. Bad playing. Bad football.”
Follow Sam Farmer on Twitter @LATimesfarmer