OTTAWA — Phil Kessel fired the puck hard into the sideboards during a lull in Penguins practice at the University of Ottawa, then bent to one knee and seemed to stew in his own frustration.

Kessel had the goal which delivered Pittsburgh their first and only win so far in the Eastern Conference final — they trail 2-1 in the best-of-seven series — but generally, he and the Penguins have been aggravated by the persistent defensive efforts of the Ottawa Senators. The highest-scoring team during the regular season, the Pens have scored only three times through three games heading into Game 4 on Friday night.

"I know that we have what it takes," head coach Mike Sullivan insisted after practice on Thursday.

A day after his team was thrashed 5-1 in Game 3, Sullivan seemed intent on trying to build confidence and lighten the mood around a team chasing a second straight Stanley Cup. He opened practice with some lighthearted drills which saw players flashing rare grins as they tried to keep pucks away from one another.

So far their experience against Canada's only remaining team has drawn mostly scowls, sighs and aggravation, including a fiery outburst from Kessel on the bench during the 1-0 Game 2 win. The Sens have simply sucked the life out of their attack with an intensely defensive approach mirroring the one which helped them capture second spot in the Atlantic division during the regular season before topping the Bruins and Rangers in the opening two rounds.

They've not only kept the Pens off the scoreboard, but limited them to just under 28 shots per-game — a far cry from the 33.5 Pittsburgh averaged during the regular season.

"It can be a frustrating system to try and get through, when we're making you dump it all the time and you're not able to float through the neutral zone with the puck, it probably gets wearing," Sens winger Bobby Ryan said.

Ottawa stacks the neutral zone with bodies, employing the 1-3-1 system which initially brought head coach Guy Boucher some recognition (both good and bad) during his time with the Tampa Bay Lightning. The approach slows down an opponent and forces them to chase down pucks in the offensive zone.

Once in the zone, the Senators are forcing the Pens to the outside. Though Pittsburgh says otherwise, dangerous scoring chances have been limited for just about everyone, including Rocket Richard trophy winner Sidney Crosby.

Craig Anderson has stopped 80 of the 83 shots he's faced.

"A lot of times we throw blankets over you and try not to give you more than five, six feet of space to make a play," Ryan said.

Crosby had his first point of the series in Game 3, a power-play marker six minutes into the third period of a game that was already over. He conceded the goal was relatively meaningless as far as relieving pressure, but expressed belief that his team was on the cusp of breaking through.

"The chances have been there, regardless of who gets them," said an upbeat Crosby in a cramped dressing room on the university campus.

Crosby, Kessel and Evgeni Malkin carried Pittsburgh's offence through the first two rounds and have combined to score the three measly goals against Ottawa. Even they haven't been all that dangerous; Malkin — the leading scorer this post-season — had just a single shot in an especially quiet Game 3.

He and Kessel have both been poked and prodded all series-long by Dion Phaneuf. The former Maple Leafs captain has been particuarly feisty against Kessel, his former Toronto teammate.

Sens captain Erik Karlsson and his partner, Marc Methot, have done an effective job containing Crosby and a rotating cast of linemates, including the rising Jake Guentzel. Whether related at all to the concussion he suffered in the second round against Washington, Crosby hasn't been near as potent as previous.

He has a goal and three assists in the six games since he returned from the head injury.

The real struggle for the Pens, however, is increasingly lacking depth beyond the stars. Last spring, the club's strength beyond those top guys was in the meaningful contributions those like Nick Bonino (18 points), Carl Hagelin (16), Patric Hornqvist (13), and Conor Sheary (10), offered.

That same quality of depth just hasn't been there this spring, whether because of injuries in the case of Hagelin, Hornqvist and injured defenders Kris Letang and Justin Schultz, or simple struggles in the case of Bonino, who has only three points in the playoffs, or Sheary, who's yet to find the back of the net.

Sullivan has also opted to play Kessel and Malkin together, contrasting the more balanced approach of last season when the two were mostly separated. And contrary to Sullivan's suggestion, Ottawa has actually had the slight edge in puck possession and scoring chances according to publicly available data.

Whether that continues will likely determine whether the Sens reach their first Cup final in a decade or the Pens go back a second straight year.

A four-time 30-goal-scorer in the NHL previously, Ryan had a sense for how the Sens clenched approach might be affecting the Penguins.

"I think it wears on you mentally and physically," he said.