A shot by the Bruins' Erik Haula gets by the Islanders'...

A shot by the Bruins' Erik Haula gets by the Islanders' Semyon Varlamov during the second period of an NHL game Saturday in Boston. Credit: AP/Michael Dwyer

BOSTON — Playoffs or not, and it’s almost certainly not, the Islanders’ players and management have shown a strong belief this is still a very good team.

Which is what made this weekend so interesting with the Islanders facing a back-to-back against two playoff-tested and postseason-bound teams.

But it was a bad Saturday afternoon for the Islanders, other than Brock Nelson becoming a 30-goal scorer for the first time in his nine NHL seasons. The Bruins pressured and forced turnovers all game, taking control with a four-goal second period as the Islanders matched their season-high for goals allowed in a 6-3 loss at TD Garden.

The two-time Stanley-Cup champion Lightning, who eliminated the Islanders in back-to-back NHL semifinals, are at UBS Arena for Sunday matinee.

“Two really good teams,” said Nelson, who knocked in a rebound with 11.3 seconds left in the first period to bring the Islanders within 2-1. “The first period, I thought we played well and matched up. Tomorrow is another big test so it will be a good chance to see what this group is all about. I know we believe in one another to have bounce-back games.”

The Islanders (28-26-9), who are still on a 7-2-1 run but had a two-game winning streak snapped, failed to move four games above NHL .500 for the first time this season. Semyon Varlamov, too often left exposed by the Islanders’ sluggish defense, made 38 saves.  Linus Ullmark stopped 24 shots for the Bruins (41-19-5), who outchanced the Islanders, 80-38.

“It felt like they were in our face, up ice,” said Zach Parise, who concluded the scoring with a power-play goal at 14:43 of the third period as the Islanders went 2-for-4 on the man advantage after  Anders Lee had made it 4-2 at 5:12 of the second period. “We weren’t very clean through the neutral zone. It didn’t feel like we could get much going through there with speed. That hurt the offense a lot.”

Defensively, the Islanders weren’t much better.

Top-pair defenseman Adam Pelech was on ice for four Bruins’ goals, including Taylor Hall’s power-play goal to make it 2-0 with 33.5 seconds left in the first period. Andy Greene was on the ice for three and coach Barry Trotz switched Pelech and Sebastian Aho to start the third period, pairing them with Greene and Pulock, respectively.

“A couple of our pairs had a rough night so we just tried to stretch it out and play 60 [minutes] understanding that we play tomorrow as well,” Trotz said.

Trotz said he considered pulling Varlamov for Ilya Sorokin  — expected to start against the Lightning — after two periods but couldn’t fault Varlamov for any of the goals.

A bigger issue was a lack of support defensively. For instance, David Pastrnak made it 3-1 at 2:13 of the second period — the first of two Bruins’ goals in the opening 3:56 of the period — after defenseman Sebastian Aho was double-teamed in the corner. Aho lost the puck battle because he had no support and the mistake quickly cost the Islanders.

“Our defense was under a little bit of duress because they forecheck well and they don’t back off,” Trotz said. “We didn’t have a lot of support [from the forwards], we turned our back on the puck. We had a little bit of swing in our D zone. Our exits weren’t always clean and when they weren’t, you get on the wrong side of people and now you’re reaching. They’re in the interior and putting it in play. We’ve got to do a little bit better job of that.”

Especially with the Lightning coming to town on Sunday.

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