Washington’s Tom Wilson is prone on the ice following a blindside hit from Vegas’s Ryan Reaves in the second period. Wilson left the game and did not return while Reaves received a five-minute major for interference and was ejected. (Ethan Miller/Getty Images)

The Washington Capitals’ previous postgame session in the T-Mobile Arena visitors’ locker room involved a champagne shower and the entire team singing along to Queen’s “We Are The Champions.” The Stanley Cup was there, and as players returned to that room for the first time, the happy memories came back, too. It was hard not to be in a good mood in there.

The frustrated expressions as the Capitals returned to that same locker room after Tuesday night’s 5-3 loss to the Vegas Golden Knights was another reminder that this is a new season. In a bruising, back-and-forth Stanley Cup finals rematch, defenseman Nate Schmidt, a former Washington player, scored the game-winning goal with 1:25 left before adding an empty-netter. The Capitals have lost two straight.

“There’s history there obviously with last year and the way they play, there’s a lot of energy in the building,” forward Brett Connolly said. “It’s a great place to play and a lot of fun, everybody’s ready to go. Physically, it was a good test for us. I thought we played good enough to win tonight, just the way it goes sometimes.”

Perhaps as expected for teams that played each other in the finals just six months ago, the game got chippy early and stayed that way. With 5:53 left in the first period, Vegas forward Ryan Reaves and Washington forward Tom Wilson collided, and Reaves laughed when Wilson dropped to the ground.

Another incident between the two in the second period had more serious consequences. Reaves delivered a late, blindside hit to Wilson, causing Wilson’s helmet to pop off. Wilson hit his head on the ice when he fell, and he was down for several seconds before he had to be helped to the Capitals’ bench. Wilson still looked unsteady on his feet as he walked down the tunnel and to the locker room, and he was ruled out for the rest of the game with a suspected concussion. Reaves received a five-minute major for interference and was ejected.

After the game, Coach Todd Reirden said Wilson will continue on the trip with the team, but he didn’t have an update on his condition beyond that.

Wilson was suspended by the NHL’s Department of Player Safety for the first 16 games of the season for an illegal check to the head during the preseason, and now that same department will review Reaves’s hit for possible supplemental discipline. Interference is rarely a suspension-worthy offense unless there’s head contact, and Reaves made contact primarily with Wilson’s shoulder.

Going into Tuesday’s game, Wilson had scored eight goals with six assists in his first 14 games back, playing on the top line and both special teams units. His return to the lineup had boosted the Capitals, who won eight of his first 10 games back, and with T.J. Oshie still out with a concussion, a serious injury to Wilson would mean the Capitals are without their two top right wings.

Washington managed just one shot on the five-minute power play for Reaves’s major, and that seemed to breathe new life into the Golden Knights going into the third period. Pierre-Edouard Bellemare and Cody Eakin scored within 16 seconds of each other to tie the score and then take a lead less than three minutes into the frame. The Capitals’ power play finished 0 for 4.

Washington recovered at even strength with 8:20 left in the third period: Center Evgeny Kuznetsov fed Jakub Vrana the puck in the high slot, and Vrana beat goaltender Marc-Andre Fleury for his second tally of the game. But forward Nic Dowd later was assessed a double minor for high-sticking, and that put the Capitals’ penalty kill on the ice without two of their top penalty-killing forwards in Dowd and Wilson. With the Golden Knights down to their last 11 seconds of power-play time, Schmidt sailed a puck past goaltender Braden Holtby’s glove for the game-winner.

“I misread it for some reason,” Holtby said. “I don’t know why. I’ll have to look at it again. It felt like it knuckled somehow. I don’t know. I’ll have to look at it again.”

The game was a slog for a Washington team that looked disjointed after it had so looked forward to its return to Las Vegas. From the short walk to the rink to the first moment they walked back into the visiting locker room to when they stepped on the ice, the Capitals were flooded with good memories of winning and celebrating their first Stanley Cup in this arena. Players joked that the locker room was in better condition than they expected after they soaked it with champagne the night they clinched the trophy.

“But that was last year,” captain Alex Ovechkin said Sunday. “This is a new year. Of course, when you coming back, you’re going to have memories, you’re going to have smile on your face, but as soon as the game starts, it’s a different day.”

Ovechkin scored his 20th goal of the season in the second period, when the arena’s live boards awarded him a fortuitous bounce with Fleury out of position. That lifted the Capitals to a 2-1 lead, and the team was hopeful that its crushing loss Sunday, when Washington squandered a four-goal lead at home to the Anaheim Ducks, would keep players from getting too wrapped up in the nostalgia of returning to T-Mobile Arena.

A brutal injury followed by a loss left a more bitter taste for players as they left the arena Tuesday night.