Washington Capitalsright wing Tom Wilson battles St. Louis right wing Scottie Upshall in Saturday’s 4-0 Blues win at Verizon Center. (Jonathan Newton/The Washington Post)

With each St. Louis Blues goal allowed, Washington Capitals Coach Barry Trotz listed the defensive mistakes that caused it. A point would’ve clinched the Presidents’ Trophy for the Capitals, but the team instead suffered one of the most lopsided losses of its season, 4-0 to the Blues.

As one-sided as the score seemed, the game itself had fairly even scoring chances, turning on a few defensive lapses by the Capitals. That was enough for a three-goal second period by St. Louis that put the game out of reach. But the team’s first shutout since Nov. 10 and a drought in five-on-five goals in the past two games left Washington similarly frustrated with its offense.

“It should’ve been a little closer than it was probably,” Trotz said.

Barring a collapse, the Capitals (53-16-5, 111 points) will almost certainly clinch the Presidents’ Trophy, likely sometime in the next week. The focus was elsewhere after Saturday night’s game.

“When you can’t bury a chance, it kind of gives the other team a little bit more jump in their step, and I think a little less for us,” defenseman John Carlson said. “It’s late in the season now, though, and we should be able to overcome things like that.”

The Capitals were pleased with their defensive effort against the New Jersey Devils on Friday night, allowing just 22 shots on goal in the 1-0 overtime win. Against the Blues, vying with Dallas for Western Conference supremacy, Washington allowed 24 shots on goal through two periods, and it allowed three goals on 16 shots in the second period.

But the defensive effort against the Devils in a win overshadowed the regulation shutout, and the two games in two nights marked the first time in more than four years that Washington had been blanked in consecutive regular season regulations.

“Obviously, we did have a lot of chances,” Jay Beagle said. “We actually played a pretty good game offensively. Just couldn’t bury. It obviously as it goes a long gets a little bit frustrating.”

Backup goaltender Philipp Grubauer got the starting nod after Braden Holtby started on Friday night. In a fast-paced and physical first period with fairly even scoring chances, Grubauer looked sharp, stopping eight shots, many from close range. But the second period included some defensive errors the Capitals could not overcome.

The Blues (45-22-9, 99 points) opened the scoring off a turnover behind the Capitals net by defenseman Dmitry Orlov. David Backes got the puck, and Grubauer stopped his shot, but the puck squirted out onto the crease. Kyle Brodziak was there and swatted the shot in with Grubauer near the opposite post.

“Our defenseman made a really, really soft play,” Trotz said. “He turns it over, ends up in the back of our net.”

The Capitals have the league’s best winning percentage when the opponent scores first, so a 1-0 lead less than five minutes into the second period wasn’t panic-inducing. But the game seemed to turn on the Blues’ second goal. With the teams playing four-on-four, Colton Parayko skated from the Blues’ end of the ice, and he released his shot just as he crossed the second blue line.

The puck split defensemen Karl Alzner and Matt Niskanen, and it got through Grubauer’s legs. Grubauer’s last start for the Capitals was similarly a rough one, as he allowed four goals on 27 shots against in a loss at the San Jose Sharks.

The Capitals challenged Parayko’s goal for offsides, and video replays showed it was close. The officials determined that Blues entered the offensive zone legally prior to the goal, so it was upheld.

“I thought the second goal, you know, changed the whole deal,” Trotz said. “. . . Grubi would like to have that one back.”

In the opposite net, St. Louis goaltender Jake Allen stymied the Capitals, making 32 saves to extend the Blues’ streak of four straight shutouts.

Less than two minutes after the second goal, the Blues extended the deficit with a tic-tac-toe sequence capped with a Vladimir Tarasenko goal from the slot, putting Washington in a 3-0 hole 12 minutes and 45 seconds into the second period. Grubauer had no chance on that one.

“The third one was just a little bit of a soft play again,” Trotz said. “Some d-zone coverage, which we lost our man one-on-one and it ends up in the back of the net.”