Goaltender Tomas Vokoun, who yielded four goals on 21 shots before being pulled at the start of the third period Tuesday, has been slumping since his 6-0 start to the season. “Whatever the reason is, I’m going to work on fixing it,” he said. (John McDonnell/The Washington Post)

Only a few months ago, Tomas Vokoun was considered the missing piece of the Washington Capitals’ puzzle, the player who would push them over the top.

So far, though, he’s been another underachieving star on a roster full of them.

He was so porous in Tuesday’s 5-1 loss to Philadelphia on home ice, Ted Leonsis called him out on his personal blog, where the owner bluntly wrote, “Our goal tending wasn’t very good” in the opening sentence of an entry entitled, “Falling Short of Measuring Up.”

Let’s get this straight at the start: The Capitals’ mystifying malaise can’t solely be placed at the foot of Vokoun’s crease. A two-goal output in the last 15 games from captain Alex Ovechkin is another big reason the team departed for Thursday’s game in Winnipeg mired in 12th place in the Eastern Conference.Alexander Semin’s season-long goal-scoring slump, as well as the injuries that have kept No. 1 defenseman Mike Green sidelined for all but eight of the team’s 29 games, also play a major role.

But it’s tough to overlook the fact that the Capitals don’t have a goaltender who can be counted upon to stop pucks in the clutch. Or, for that matter, in the first period of a big game on home ice, with a clear look at the shooter, as we all witnessed Tuesday.

NHL goalies are expected to stop Scott Hartnell’s harmless-looking wrist shot from the circle 10 times out of 10. Vokoun allowed it to trickle through his pads, continuing a trend of allowing soft goals at precisely the wrong moment.

Until Hartnell scored, the Capitals had been holding their own against the East’s top team. After it, the Verizon Center crowd went silent (except for the large contingent of Flyers fans) and shoulders on the home bench sagged.

A veteran-laden team should possess enough mental fortitude to overcome a soft goal. But the Capitals are a fragile group these days, and goals such as Hartnell’s can easily shatter the team’s collective confidence.

There don’t appear to be any quick fixes.

Backup goalie Michal Neuvirth has worse numbers than Vokoun, his 3.73 goals against average and .875 save percentage ranking last among qualifying goalies, according to NHL.com. Touted minor league prospect Braden Holtby, meantime, hasn’t been much better in Hershey. The 22-year-old has an .898 save percentage and 2.60 goals against average, not to mention the Capitals are up against the salary cap, which complicates matters.

Given all that, the Capitals’ best hope is that Vokoun works his way out of the slump, just as he has done at times throughout his 14-year career. He entered the season tied for the best save percentage (.922) in the NHL since the lockout for a reason.

“I haven’t gone through it in a while,” he said. “But everything can be fixed.”

On Wednesday, Vokoun took the first step: He admitted there is a problem.

“I don’t think I give [up] as many soft goals in a month [that] I give up in threeyears,” Vokoun said. “It’s such a fine line.

“Sometimes you [are] just one step [slow], too early down, or you don’t track the puck like you’re supposed to. Unfortunately for goalie, you make one mistake in the game, or two, and it looks terrible.”

After yielding four goals on 21 shots before being pulled at the start of the third period, the 35-year-old’s goals against average dropped to 2.81 (31st) and his save percentage fell to .906 (25th).

“I just don’t feel comfortable out there,” he said. “Some games, we win the game but it’s still a battle. For whatever reason I don’t have the comfort level I’ve had in past years and it shows. Some of the goals, I would put in the ‘terrible’ column. They are tough goals on a team, and we’re not exactly the most confident right now.”

Vokoun refused to use his difficult personal situation as a crutch.

After signing a one-year, $1.5 million contract in July — a $4.8 million pay cut from the salary he earned in Florida in 2010-11 — he moved to Washington without his wife and two young daughters, leaving them behind in Fort Lauderdale, Fla., because of his uncertain future. It is the first time the Vokouns have been separated for any length of time.

“That’s my problem,” he said softly. “I can’t . . . I’m paid to do job and I’m a professional. I have to be able to deal with it. It was fine at the start and now it’s kind of, you know . . .”

As tough as the past several weeks have been for the Capitals and Vokoun in particular, forward Brooks Laich said the dressing room hasn’t given up on him.

“He’ll tell you it wasn’t his best game,” Laich said of the loss to Philadelphia. “He’s been a professional for a long time, and he’s going to bounce back from it.”

Vokoun hasn’t given up, either. He said he plans on studying video from October, when he opened the season 6-0, and redoubling his efforts in practice.

“Whatever the reason is, I’m going to work on fixing it,” he said. “Hopefully next game will be the first step to a whole lot better performances than I’ve been giving lately.”

The Capitals — and any hope they have of making a run this season — are depending on it.

Capitals notes: General Manager George McPhee said Green is expected to join the Capitals in Colorado later this week after the defenseman met with a specialist about the lingering right groin muscle strain that has kept him out of 15 consecutive games. . . .

Injured players Jay Beagle (concussion) and Matt Hendricks (right knee) are traveling with the team on its trip, which begins Thursday in Winnipeg.