Bruins fans were treated to likely the team’s best 60 minutes of the season Saturday night in the 3-1 win over the Red Wings.

At 2-5-1 on TD Garden ice into Tuesday night’s tangle with the San Jose Sharks, would the team win two in a row at home for the first time this season?

“This playing once in a while in games is just not gonna cut it in this league,” Claude Julien said postgame about his team’s deplorable 5-4 loss to the Sharks. “We can talk about a lot of things, but the most important thing is [to] go out there and do it and show it.”

It didn’t start good when Joe Pavelski scored just 42 seconds in. But Tyler Randell tipped a Dennis Seidenberg shot by Martin Jones at 9:20 for his third goal of the season.

Then Boston’s league-best power play went to work. Brad Marchand scooped up a Zdeno Chara wrister and backhanded it past Martin Jones at 11:50 for the 2-1 lead; Brett Connolly assisting.

Joonas Donskoi responded at 15:08 with a soft shot to Rask’s left to knot the score at 2-2.

Loui Eriksson put Boston back in front, 3-2, at 1:53 of the second period; David Krejci and Seidenberg assisting. But Tuukka Rask got hung out dry when Melker Karlsson blew one by Rask at 5:56.

The Bruins then fell apart by doing what they do so much of so far this season; taking bad penalties — with the worst penalty-killing stats in the league.

First, a bench minor for too many men on the ice with Patrick Marleau putting the Sharks up, 4-3, at 8:56, when he put one under a sprawled Rask. A Claude Julien challenge for goaltender interference went for naught.

“Tuukka [Rask] came to the bench,” Julien said, “and said that his stick was in his blocker and prevented him from getting over there quick enough.”

Old friend Joe Thornton scored just 25 ticks later at 9:21 with Ryan Spooner in the box – and the Sharks had a two-goal lead.

Randell followed with two for roughing at 11:16. Three penalties in three minutes that spelled disaster in the Bruins’ worst period of the year. Five goals on 13 total shots on Rask to that point; most of them hardly highlight-reel stuff.

“I think it’s more about the fact that we gave up a power play goal,” Julien said, “which was from a mental mistake that should never happen.”

In what would be the regulation shootout of the season so far, Boston’s vaunted power play went to work in the final period with Bergeron scoring at 6:28 to narrow the game to 5-4; Spooner and Krejci assisting.

Too little too late. The Bruins could not get the equalizer – especially when the better part of the last two minutes were shorthanded with Brad Marchand in the penalty box for high sticking.

“Those kinds of things, you can’t hold players by the collar on the bench,” a visibly upset Julien said postgame. “I don’t have enough hands for that. It’s called focus, the kind of mistakes that we’ve made, and even the stuff that we talked about, how can you be good in one game and not the other?”

Here’s what we learned from Tuesday night’s meltdown.

The Bruins have a (bad) habit of being good in one game and not the other

Enough said.

The penalty kill failed miserably (again) while the captains struggled shorthanded

Before the second period meltdown, Boston had the worst penalty kill in the NHL. By the time the dust cleared in the second period, it grew even worse with 19 goals allowed in 61 opponent opportunities so far.

To add insult, Chara and Patrice Bergeron were on the ice for four of the Sharks’ first five goals – and all three in the second period.

The Rask task remains a serious work in progress

As Rask goes, so go the Bruins. Boston’s go-to guy was 2-2 his last four games; his GAA is a very respectable 2.03. Tuesday’s 5-goal total put a dent in those stats, not to mention it was a season high allowed.

After giving up five goals in 13 shots, he settled in and pitched a shutout the next 15 shots.

“You look at most of those goals,” Rask said after, “how they got scored on. I think it’s just lack of focus for the most part. We weren’t sharp today.”

When Brad Marchand scores, the Bruins won

Until Tuesday night. The Black and Gold were 7-0-1 when Marchand scored a point.

Time is on his “Seid.”

Dennis Seidenberg celebrated his 700th NHL game Tuesday night (343 with Boston). In his first two games back from his second surgery in two years, he logged 15:34 and 19:05 ice time, respectively. Against the Sharks, it was 19:54 as he rebounds to a top-3 D-man on the Bruins blue line while chipping in with his first points of the season.

(Adam McQuaid, quietly assuming a top spot among the team’s blue-line depth chart, played in his 300th career game.)

Those Two- No. 1’s in the Lucic trade

The Bruins got goaltender Martin Jones, defenseman Colin Miller and Los Angeles’s first-round pick back in the major pieces of the Milan Lucic trade with the Kings back in June. GM Don Sweeney then promptly packaged Jones to the Sharks for their first-round pick this June. All Jones has done is to become the Sharks starting goalie with eight of San Jose’s nine wins into Tuesday night and a 2.11. Make that 9 of 10 in his first career start against Boston.

The more he wins, the lower that draft Bruins pick plunges come June.

Ten years later, Thornton can still bring it

At 36, Joe Thornton is celebrating the 10th anniversary (November 30, 2005) of his heralded trade by scoring the winning goal. His line accounted for seven points.

“We weren’t able to handle that line tonight,” Julien said. “We didn’t do a good enough job against that line, and they ate us up.”

“Sloppy tonight, sloppy,” Julien assessed about Tuesday’s debacle. “Really that’s the only word I can find right now.”

He and his charges have 48 hours to shore things up. Thursday, Minnesota comes town for the fourth game of the home stand. The Bruins are 1-2 so far – and 2-6-1 overall at home.

“Tomorrow’s gonna be a work day again,” Rask said, “and we have to fix things and hope that next game we play is gonna be a good one.”

That work will be tempered with Julien’s ire.

“We have to deal with certain things I plan on dealing with internally,” Julien said. “This is where part of my job has to be worked on in the dressing room.”