BOSTON — With their second straight Presidents’ Trophy already in tow, the Washington Capitals didn’t have all that much to play for Saturday at TD Garden.

Standings-wise, that is.

The Capitals, knowing they could help secure a first-round playoff matchup against Boston, continued their dominance of the Bruins with a convincing 3-1 victory — their ninth in a row in the series over three seasons.

“Obviously we were not playing for any position or anything. We were just playing trying to play the right way,” Washington coach Barry Trotz said after the game. “I think we’ve had good success against these guys this year in terms of managing our game when we had to.

“I just thought we were real professional today with our approach.”

The Capitals have outscored the Bruins 30-11 during a nine-game streak that started with three Braden Holtby shutouts and represents three straight season series sweeps.

Boston, losing its second straight to end the regular season but in the playoffs for the first time in three years, lost any chance of home-ice advantage in the first round when Ottawa beat the New York Rangers on Saturday. But a win would have wrapped up the third seed and a first-round series against the Senators.

With the loss, the Bruins will play either Ottawa or the Capitals in the first round — depending on what Toronto does in two weekend games. The Maple Leafs needed at least three of a possible four points to pass Boston and play Ottawa.

Bruins interim coach Bruce Cassidy, who fell to 18-8-1 since taking over for the fired Claude Julien, wouldn’t state his preference for an opponent. But he does think Washington is a better team than Ottawa and hinted the Bruins are better off staying in the Atlantic Division as the three seed (and staying away from Washington, the Pittsburgh Penguins and Columbus Blue Jackets).

The Capitals have won four straight, 10 of their last 11 and are 11-1-1 in their last 13. They will likely play either Toronto or Boston, but the Tampa Bay Lightning and New York Islanders could be in the mix if the Maple Leafs drop their final two games.

Justin Williams had a goal and an assist and backup goaltender Philipp Grubauer (13-6-2) made 21 saves for the Capitals, who answered a second-period goal by Boston’s Colin Miller with one by defenseman Kevin Shattenkirk 56 seconds later.

Williams, who caused a goal to be disallowed because he was in the crease, followed 3:01 later to make it 3-1.

“There’s a lot of positives off of that (game),” said Trotz, who before the game said he thought a good effort was important “if we end up meeting each other.”

Marcus Johansson, playing in his 500th NHL game, scored the first Washington goal.

“It was probably a pretty frustrating game for them,” said Johansson. “They didn’t get too much.”

Anton Khudobin made 21 saves in two periods before leaving because of illness. He had his six-game winning streak stopped.

The Bruins played their second straight game without the suspended Brad Marchand and scored two goals in the two games without their 39-goal scorer, who was especially missed in Thursday’s shootout loss to Ottawa. Torey Krug, Boston’s fastest defenseman, suffered a knee injury in the first period of that game, also hurting the attack.

On top of that, Bruins rookie defenseman Brandon Carlo left the game in the first period with an upper body injury after he was crunched face-first into the boards by Washington captain Alex Ovechkin.

Carlo was shaky as they led him off the ice with what was later called an upper-body injury. Ovechkin knocked Columbus defenseman Zach Werenski out of the game on a similar hit April 2 and Werenski is still out. There was no penalty on either play.

Cassidy thought while there was no intent, the hit should have been whistled for a penalty.

“I didn’t like it. To not have a two- or five- (minute penalty) I think is wrong,” he said.

NOTES: C Jakob Forsbacka-Karlsson, signed recently by the Bruins, made his NHL debut because Brad Marchand is suspended and Noel Acciari is injured. … Bruins D Torey Krug is out with a knee injury. … Marchand and RW David Pastrnak both won two season awards pregame. … The Caps, who host the Florida Panthers on Sunday, were missing D John Carlson (lower body) and RW Brett Connolly (illness). … C Paul Carey, a Boston native, made his TD Garden debut for Washington. … Tom Brady was at the game and shown on the big board. … Washington D Brooks Orpik played in his 900th NHL game and LW Marcus Johansson played in his 500th, the latter all with the Caps. … The Bruins held their “Shirts Off Their Backs” giveaway with the fans after the game.