KANSAS CITY, Mo. — Jared Goff threw for 253 yards and a touchdown, new Lions running back David Montgomery ran for the go-ahead score with 5 minutes, 5 seconds remaining and Detroit held on for a sloppy 21-20 victory against the Super Bowl champion Kansas City Chiefs in the NFL’s season opener Thursday night.

Amon-Ra St. Brown had six catches for 71 yards and a score, and Lions rookie Brian Branch returned Patrick Mahomes’ first pick in an opener 50 yards for another touchdown, helping the Lions snap the Chiefs’ eight-game Week 1 winning streak.

The Lions were trying to run out the clock when Goff had a fourth-down pass near midfield batted down with 2:30 left, giving the Chiefs a chance. But they made a mess of it: Kadarius Toney dropped a potential 20-yard gain, a deep completion was called back for holding, Skyy Moore dropped a pass and a false start left Mahomes heaving a fourth-and-25 throw downfield.

When it fell incomplete and the Lions took over, Montgomery ran for a first down that allowed them to run out the clock.

Mahomes threw for 226 yards and two touchdowns despite his receivers dropping a slew of passes. He also was the leading rusher for the Chiefs, whose self-inflicted wounds proved too much to overcome.

There had been equal parts anticipation and anxiety leading up to the game in Kansas City, Mo., where the Chiefs celebrated their previous Lombardi Trophy in the midst of a pandemic and only about 18,000 fans were able to join in the revelry.

Hundreds began tailgating outside the Arrowhead Stadium parking lot Thursday, waiting for the gates to open 14 hours before kickoff, and NFL Commissioner Roger Goodell joined several celebrities to see the Chiefs raise a championship banner.

That was the anticipation. The anxiety came from the absence of Chiefs tight end Travis Kelce and fellow All-Pro Chris Jones, who is in the midst of a contract holdout. The defensive tackle was expected to miss the opener, but Kelce had only been questionable since Tuesday, when he hyperextended his knee in the final full practice before game day.

The Lions scored first in a showdown of two of the league’s top offenses from a year ago. Goff took advantage of a clean pocket, marched downfield and found St. Brown with a 9-yard touchdown pass.

The Chiefs answered with Mahomes finding five wide receivers, the last of them rookie Rashee Rice, who atoned for an earlier drop by snaring a short touchdown pass to knot the game at 7.

It remained that way until Lions coach Dan Campbell made a questionable decision late in the half.

The Chiefs were facing fourth-and-2 near midfield but had been called for holding, and rather than decline it, Campbell chose to push them back. Mahomes responded to third-and-17 by hitting Marquez Valdes-Scantling with a 24-yard strike. He added a 26-yard pass to Justin Watson, then hit Blake Bell with a short TD throw to give the Chiefs a 14-7 halftime lead.

With the Lions offense going nowhere, the defense stepped up. Branch caught a pass that bounced off Toney’s hands — he had several drops in the game — and found nothing but 50 yards of grass separating him from the end zone and a 14-all tie.

Up to that point, Mahomes had thrown 20 touchdown passes and no interceptions in five-plus season openers.

The Chiefs tacked on two field goals, but the missed chances to get into the end zone proved costly. The Lions followed up Harrison Butker’s second field goal by driving 75 yards, twice converting on third down, with Montgomery capping the march with a 9-yard touchdown run.

The Lions’ Marvin Jones fumbled away a good scoring chance in the second quarter when Trent McDuffie knocked the ball out deep in Chiefs territory. It was the veteran wide receiver’s first fumble in his 12-year career and came on his 563rd touch, the longest active streak in the NFL.

Kelce had a bone bruise and some swelling in his knee, though tests taken after the injury in practice showed no ligament damage. He went through a workout early Thursday to see whether he could move well enough to play, but Chiefs coach Andy Reid and trainer Rick Burkholder decided to give Kelce time to recover with their next game 10 days away.