DETROIT -- The Pittsburgh Penguins believe they are seeing cracks in Detroit's wall of perceived invincibility after four games of a very even series.

In the third period of both Games 3 and 4 -- back-to-back 4-2 wins at Mellon Arena -- some Penguins looked across the ice and saw the guys in white sweaters
with hands on knees, laboring to get air in their lungs.

"I think maybe we swung momentum to our side and, if it was up to us, we'd like to get right back at it (Friday)," Pittsburgh defenseman Brooks Orpik said
after Thursday night's victory.

Instead, the Penguins will have to wait until Saturday for Game 5 (8 p.m. ET, NBC, CBC, RDS) at Joe Louis Arena to continue riding the wave of momentum they
have created in the past two games.

And, as they wait for Game 5, they will certainly remember the images of some of the Detroit players looking gassed at points of Game 3, as well as Game 4.
They will also hear the sound bites of hockey analysts, like Ed Olczyk on Versus, offering up the opinion that some of Detroit's older players looked tired
and may have hit a wall after playing four games in six days.

One of those players is Henrik Zetterberg, Detroit's No. 1 center.

"You look at Zetterberg out there and he looks so tired out there," Orpik said. "He's playing 25 minutes a game. I think he even admitted it. He's chasing
Sid (Crosby) around the whole time and that takes a lot out of him. Maybe it keeps Zetterberg off the scoreboard, too, because he is so drained."

With Detroit center Pavel Datsyuk out of the lineup throughout the first four games of the series because of a foot injury, Zetterberg has been used
extensively in a matchup against Sidney Crosby and Pittsburgh's top line. Datsyuk may be back in Game 5.

But for now, Zetterberg has logged a mountain of minutes, topped by more than 24 minutes in Game 3. He is averaging a whopping 23:15 per game. Orpik says
those are hard minutes.

"We get to do it in practice every day and it is no fun," Orpik said. "Sid's just so unique, his feet never stop, his motor never stops. He's relentless.
He's not tall, but he is so strong on his feet. He's a real physical player. He might not run you over but just battling with him takes a lot out of you.

"He's one of their offensive guys. At the end of the game, they need him to score goals and I think Sid has taken so much out of him, I think it is tough
for him to get going."

The numbers bear that out to a degree.

Zetterberg had an assist in Game 4, but also managed just one shot. He has 1 goal and 3 assists in the series and just 10 shots.

Crosby tried to put the kibosh on the notion that he is tiring out Zetterberg, even after he had his best game Thursday night, scoring the game-winning goal
and adding an assist.

"I'm just trying to battle," said Crosby, adding he does not feel Zetterberg is getting worn down. "That's what it comes down to. It's tough to get any
space out there for both teams. Both teams are pretty committed defensively. You know, you just fight for those chances and when you get them you try to
take advantage of them. 

"He's a great player. And he's battling, too."

But it is not just Zetterberg. The Penguins are actively trying to erode Detroit's will by playing a physical, grinding game. They have made it a priority
to take the body whenever possible. Forwards Chris Kunitz and Matt Cooke and Orpik have been at the forefront of the checking onslaught

Through four games, Pittsburgh has thrown 138 hits, an average of 34.5 per game. Detroit is in the mix, though, with 127 hits of its own. That's a lot of
body contact, however you cut it.

"It's a seven-game series, and we've got to play it like we're initiating and investing for seven games," coach Dan Bylsma said before Game 4.

After Game 4, the Penguins believe they have tangible evidence that the investment is paying dividends.