LAS VEGAS — As Tyson Fury and Deontay Wilder prepared to put on one of Sin City’s biggest boxing matches in years Saturday, Bears coach Matt Nagy gathered his players at their hotel. The game Sunday against the Raiders, he told them, was going to be a brawl.
‘‘This is going to be a fistfight in a back alley,’’ Nagy told his team.
The Bears were ready. In one of the most meaningful victories in Nagy’s 3 1/2-year coaching tenure, rookie quarterback Justin Fields proved his toughness over and over again. The Bears’ running game bullied the Raiders, even with David Montgomery on injured reserve. Most important, the Bears’ defense hammered the NFL’s top-ranked passing offense in a 20-9 victory at Allegiant Stadium.
‘‘It was huge,’’ inside linebacker Roquan Smith said. ‘‘Not many people had us doing what we did.’’
This was the Bears’ defense we’ve been waiting for, the kind that can take over a game, one that punches back.
‘‘We just wanted to dominate,’’ safety Eddie Jackson said.
The Raiders averaged 4.3 yards per play, the fewest the Bears have allowed all season.
Five of the Raiders’ 10 drives yielded eight yards or fewer. Two ended on downs. In the second quarter, Smith stuffed running back Josh Jacobs on fourth-and-one. On the stop that sealed the game, the Bears — leading by eight with two minutes left — forced an incompletion on fourth-and-five.
Raiders quarterback Derek Carr, who led the NFL in passing yards entering play Sunday, went 22-for-35 for 206 yards and an interception. His 67.1 passer rating was the 15th-worst of his career (115 starts).
Carr was sacked three times. Outside linebacker Khalil Mack, whom the Raiders traded to the Bears for a pile of draft picks in 2018, had one and a second on a two-point conversion that didn’t count statistically.
‘‘He made them regret everything,’’ Jackson said. ‘‘Made them regret not wanting to keep him. You know, Mack’s our leader. He’s had games like this. We fuel off that.’’
The Bears said Mack was unavailable to talk after the game. He made no secret of his motivation to play his old team, particularly after he was practically shut out against the Raiders two years ago in London.
Jackson said the Bears wanted revenge against Raiders coach Jon Gruden, who mocked ‘‘Club Dub’’ in his locker-room speech after the game in London.
‘‘Fuel to the fire,’’ he said.
Nagy pointed to the long, angry airplane flight home to the United States after that game.
‘‘I don’t care what anybody says, you remember that,’’ Nagy said. ‘‘[Mack] was part of that, and he understands that. I think all of our guys . . . it’s the mindset of making sure our guys know that we weren’t coming in here to play; this was going to be a fight. He knew that.
‘‘And so Khalil’s in a leadership role to make sure other guys see how he plays in this moment.’’
Playing with inside linebacker Danny Trevathan in a part-time role but without injured defensive lineman Akiem Hicks, the Bears seem to have found a formula — albeit one as old as the franchise itself.
‘‘I feel like that’s been a Bears thing,’’ Jackson said. ‘‘That’s Chicago Bears: The defense goes out there and plays, trying to hold them to no points.’’
Or nine. Only three times in the Nagy era had the Bears allowed fewer points. That dominance, more than any other reason, is why the Bears are in a markedly different place than they were eight days earlier.
Nagy was asked what he had learned about his team since its embarrassing loss to the Browns in Week 3.
‘‘We fight, plain and simple,’’ Nagy said. ‘‘I don’t make it hard. I just make it real simple. And these guys, they fight.’’