The Penguins played the fourth-longest game in franchise history Thursday night at Mellon Arena.

It was an epic game, one most of them won't forget anytime soon.

No matter how hard they try.

Ottawa defenseman Matt Carkner scored at 7:06 of triple-overtime to give the Senators a 4-3 victory in Game 5 of their opening-round playoff series against the Penguins. The Senators' victory prevented the Penguins from locking up a spot in the second round of the Stanley Cup playoffs and sent the series to Game 6 at 7:08 p.m. Saturday at Scotiabank Place.

Game 7, if necessary, will be Tuesday night at Mellon Arena.

The official score sheet shows that Carkner, a former Penguins minor leaguer, won the game for Ottawa when his slap shot from the right point caromed off Penguins winger Matt Cooke and sailed past goalie Marc-Andre Fleury at 11:40 p.m.

The Penguins, though, are convinced that the game was lost hours earlier, when they were near-no shows for the start of the game, spotting Ottawa a 2-0 lead that took most of the evening to overcome.

"Obviously, it's disappointing," Penguins defenseman Kris Letang said. "We battled back, but the main point was that we didn't show up in the first."

The Penguins had said for two days that they expected the Senators to compete and battle and scrap on every shift in Game 5, and there was no reason to question that assessment early in the game.

"They came out and played very well," Penguins coach Dan Bylsma said.

Ottawa got its first goal when Mike Fisher deflected an Erik Karlsson shot past Fleury on a power play at 10:25 of the first, and Jarkko Ruutu made it 2-0 68 seconds later by punching in a rebound from the front edge of the crease.

"I think we should realize that the way we started the game is unacceptable," Cooke said.

Trying to overcome that deficit was a challenge not only because of Senators goalie Pascal Leclaire, who finished with 56 saves -- "He played outstanding," Senators coach Cory Clouston said -- but because of his teammates' commitment to keeping pucks away from the net. Ottawa recorded 46 blocked shots, which is two more than the Senators managed to throw at Fleury.

"They did a remarkable job of making it difficult to get [the puck] through," Bylsma said.

Letang, however, found a way on a power play at 18:05 of the first. An Evgeni Malkin feed ticketed for Bill Guerin in the slot slid all the way to the left circle, where Letang collected it before throwing a shot behind Leclaire for his second goal of the series.

That goal rejuvenated the standing-room crowd of 17,132, and the Penguins dominated play during much of the second period as evidenced by their 19-5 advantage in shots.

It was not until 18:34, however, that they managed to pull even on a controversial goal by Chris Kunitz.

Kunitz chopped in a Sidney Crosby rebound from the right side of the crease, but referee Brian Pochmara gestured emphatically that the goal was being waved off because the net had been dislodged before the puck entered it. After a lengthy video review, it was determined that the goal was valid.

Crosby gave the Penguins their only lead of the game, 3-2, on a spectacular effort at 9:01 of the third, sweeping a shot past Leclaire from below the hash marks while Zack Smith of the Senators dragged him to the ice.

The goal was Crosby's 13th point, matching his personal-best in a series. He put up the same total in seven games against Washington during the second round in 2009.

That goal not only gave Crosby an entry in his personal record book, but the Penguins a reason to believe they might be closing in on a berth in Round 2.

"You think you have the momentum," Letang said. "But things change around really quick in the playoffs."

In this case, it took all of 83 seconds, because that's how much time passed between Crosby's goal and one Ottawa's Peter Regin got by hammering a slap shot past Fleury from the slot.

Regin's goal was the last by either team for a couple of hours, until Carkner put Game 6 on the Penguins' weekend schedule. And raised the issue of how the Penguins will deal with such a physically and emotionally draining defeat.

Crosby, predictably, downplayed such concerns.

"It's a loss," he said. "We could have lost, 10-1. We could have lost, 2-1, in regulation. It doesn't matter.

"If we play the right way -- and we feel like we did -- we feel like we'll get rewarded for it."