ST. LOUIS — Washington Capitals defenseman Matt Niskanen stayed with Blues forward Vladimir Tarasenko as he drove to the net. Tarasenko managed to get a backhanded swat of the puck at close range, and goaltender Braden Holtby pivoted for the puck to bounce off his pad. But the rebound took an unlucky bounce off Niskanen’s skate, launching the puck up and toward Holtby again.

Holtby kicked out a leg to shift over to the post while swinging his glove up, deftly catching the puck a split-second after he made the first save. And so, the Blues came up empty after nearly four minutes of power-play time in the third period, a critical moment for a highly motivated St. Louis club that ended up losing to a Washington team playing on tired legs and with its playoff position already secure.

Holtby made 34 saves in the Capitals’ 4-2 win Monday, and Washington made a statement that, although it clinched the Metropolitan Division on Sunday, it wants to enter the postseason playing well.

“We knew St. Louis had a lot to play for, and we wanted to win as well,” center Nicklas Backstrom said. “This is a playoff-type game, and it’s going to be tight games like this for 60 minutes. It’s just the way it is right now, but it’s fun, too.”

This game seemed destined to be a “schedule loss” before it started. The Capitals played in Pittsburgh on Sunday, beating the Penguins in an emotional rivalry game that clinched the division crown for a third straight season. That meant Washington didn’t have anything to play for in St. Louis less than 24 hours later, and the Blues entered the contest just one point out of the Western Conference’s second wild-card spot, desperate for a win.

“It doesn’t mean you take the foot off the gas,” Capitals Coach Barry Trotz said before the game.

Fourth-line center Jay Beagle played just 3:22 of Sunday’s game, out with an undisclosed upper-body injury for the final two periods and then again Monday. Right wing T.J. Oshie didn’t miss a shift in Pittsburgh, scoring Washington’s first goal, but after he missed the last 9:55 of Friday night’s game with a lower-body injury, the Capitals decided to scratch him against St. Louis, his former team. The luxury of having already clinched the top seed in the division is that Washington can be cautious with its roster in this final week of the regular season.

Wingers Shane Gersich and Alex Chiasson drew back into the lineup after being scratched the past two games. Trotz has said he’s undecided on which forwards he’ll play in his bottom-six forward corps in the playoffs, creating a competition, especially for the four spots on the wing.

Gersich played so well that Trotz said the rookie will play in Washington’s final two regular season games, and he’s making a case for himself. Chiasson took advantage of his opportunity with a second goal and eighth point in his past 11 games.

The Blues took the lead just 3:38 into the game, when Tarasenko skated around Washington’s Dmitry Orlov before unfurling a wrist shot from the slot. But Backstrom tied the score less than a minute into the second period with his 20th goal.

Less than two minutes later, Jakub Jerabek’s stretch pass sprung Chiasson for a breakaway, lifting the Capitals to a 2-1 lead. Andre Burakovsky then capped the Capitals’ three-goal period with a highlight-reel, between-the-legs move around Blues defenseman Vince Dunn before beating goaltender Jake Allen.

“I was just trying to get a puck around him,” Burakovsky said. “I wasn’t really thinking too much. It just happened. It worked out pretty good. I got lucky on the shot, too. . . .

“They had a lot to play for, and I think we’re just trying to put our game together. Obviously, we’re not taking our foot off the gas. We’re just going to keep going. The playoffs are right around the corner, so we’ll battling just as hard for every game and every point as midseason. It doesn’t matter if we’re already clinched the division or what.”

Alex Ovechkin added an empty-net, power-play goal late in the third, his 46th of the season.

Burakovsky’s goal would have been the play of the game had it not been for Holtby’s glove save in the third. The Capitals have been rotating goaltenders from one game to the next as Trotz has yet to settle on a postseason starter. Philipp Grubauer made a statement with his 36-save performance in the 3-1 win in Pittsburgh, and Holtby was back in net against the Blues. Just two years ago, Holtby won his 48th game of the season, tying Martin Brodeur for the NHL single-season record, here at Scottrade Center.

This campaign will be Holtby’s first in four years under Trotz that he hasn’t reached the 40-win plateau — he went 2-5-2 in February — but his play has recently improved. Entering Monday’s game, Holtby had won three of his past four starts, with a .907 save percentage and a 2.75 goals against average in that span. With Washington up by two goals in the second period, Patrik Berglund narrowed the deficit when his shot deflected off Niskanen’s shin, changing directions as it got past Holtby. He didn’t let another puck past, making a statement of his own with the playoffs near.

“Previous years, we were talking about how we can’t wait for the playoffs in January,” Holtby said. “Now, we’ve just been focusing on the process, and all of a sudden they’re almost here. We can just roll right in and keep playing good hockey. That’s our goal.”

More on the Capitals: