BOSTON — Clarke MacArthur spent almost two full seasons recovering from a concussion, wondering if he would ever be able to return to the Senators.

“There’s nothing like living in the NHL and living in these playoffs,” he said after scoring a power-play goal 6:30 into overtime to help Ottawa beat Boston 3-2 in Game 6 on Sunday and advance to the second round of the Stanley Cup playoffs.

“It (retirement) is something everyone’s going to have to deal with one day,” said the 32-year-old forward, who was injured in the fourth game of last season and didn’t come back until four games left in this one. “But I want to stretch it out as long as I can.”

Bobby Ryan and Kyle Turris scored five minutes apart in the second to give the Senators a 2-1 lead, and Craig Anderson stopped 28 shots for Ottawa. The Senators, who hadn’t won a postseason series for since 2013, will play the New York Rangers in the second round.

Tuukka Rask made 26 saves for the Bruins, who got goals from Drew Stafford and Patrice Bergeron. The Bruins did not get off a shot in the extra period — the fourth overtime game of the series and the 17th of the NHL playoffs, tying the record for an opening round.

“We came in here, took a deep breath (and) realized that, ‘Hey, tie game. Next shot wins. Let’s get back to business,'” Anderson said. “That’s all we did.”

MacArthur sustained a concussion on Oct. 14, 2015 — Game 4 of last season — and hadn’t played since, missing 156 games before he finally passed a baseline test in the last weeks of this season and was cleared to return. He played in only four games this year, without recording a point.

“You’ve been off for a couple of years and you’re thinking, ‘Yeah, I should make this play’ or ‘I should be able to do that,'” he said. “I’ve just been trying to stick with it and be patient, and you know it’s slowly coming.”

MacArthur scored in Game 2 of the series, and then got past David Pastrnak on his way into the Bruins’ zone in overtime, tempting the Boston forward into pulling him down from behind. Just 36 seconds into the power play, MacArthur grabbed a puck that deflected off Tuukka Rask and beat him on the rebound for the series-winner.

“It was off his paddle and went right to me. I was just lucky enough to be in the right spot,” MacArthur said. “You get opportunities like that to put them away, you’ve got to put them away. It’s just awesome that we were able to.”

The Bruins made the playoffs for the first time in three seasons, rallying after firing the winningest coach in franchise history and the one that led them to the 2011 Stanley Cup title. They went 18-8 after Bruce Cassidy replaced Claude Julien, but lost their last two to finish third — behind Ottawa — in the Atlantic Division.

That left them matched up with the Senators in the first round — a bad draw against a team that beat them all four times in the regular season and six straight overall. After winning Game 1, Boston lost three in a row before forcing a fifth game with a double-overtime victory on Friday night.

Cassidy, who served out the season as the interim coach, said he “absolutely, 100 percent” wants to be back.

“That will be determined by management, whether I continue to be the head coach,” he said. “And what players will be here will be determined by management.”

The Bruins were hit with three delay of game penalties in the first period for sending the puck over the glass, but on none of those power plays did Ottawa even manage as much as a shot on goal. Instead, Boston took a 1-0 lead with just under two minutes left in the first when Stafford converted on a tripping penalty against Mark Stone.

But Ryan tied it for Ottawa on a power play early in the second, then Turris gave the Senators a 2-1 lead about five minutes later. It stayed that way until Bergeron tied it about two minutes into the third.

NOTES: The Bruins were without F David Krejci, who injured his knee in a collision with Senators D Chris Wideman in Game 5 on Friday. … Ryan leads Ottawa with four goals in the playoffs. He also assisted on the game-winner.