The Dallas Stars continue to have one of the best penalty-killing units in the NHL.

But if Dallas keeps testing the PK the way it has the last three games, then cracks are going to start showing.

Ottawa scored a third-period power play goal that was the game-winner in a 4-2 victory over the Stars on Friday at American Airlines Center.

Dallas, which entered the game ranked fourth in the NHL on the penalty kill, pretty much took the Senators out of their game while strangling 9:13 of man advantage time off the clock. But the one slip was the key in what ended up being a very close game.

"You want to be disciplined, especially against a team likes this," Stars captain Brenden Morrow said.

The Stars have run into a bit of a buzz saw in the form of two talented teams in San Jose and Ottawa their last two games. Both scored on the power play and both defeated the Stars at home.

That takes quite a bit of bite out of a six-game road trip in which Dallas collected eight points. The Stars are now 2-4-0 in their last six contests.

"It's disappointing," said goalie Mike Smith, who stopped 16 of 19 shots. "Obviously, we came in off the road and we were feeling pretty good, and now after these two losses, we're feeling pretty bad."

The Stars slipped to 15-11-4, including a 7-5-2 mark on home ice. The Senators won for the second time in a row and moved to 18-7-3 (8-2-2 on the road).

"You hate losing, that's the bottom line," Stars coach Dave Tippett said. "We battled hard, and we couldn't get a break – from the calls to the bounces around the net."

Niklas Hagman took a five-minute major for boarding in the second period, and the Stars were able to kill that penalty. However, they allowed the game-winner after Stu Barnes was called for a double-minor on a third-period high stick. The linesman made the call on Barnes' penalty after a significant delay because the referees had missed the call.

Then, after the Stars scored to close the gap to 3-2 with 1:49 remaining, Stars forward Jussi Jokinen appeared to be high-sticked by Daniel Alfredsson, but no call was made.

"I find it amazing they saw the high stick on Barnes, but not Jussi late in the game," Tippett said. "Those are frustrating. They stop the game to call one, and then they miss a blatant one."

The Stars carried much of the play in the first period and used the power play to their advantage. Steve Ott, Jeff Halpern and Mike Modano created some scoring opportunities early, and Ott drew a four-minute power play from Chris Neil after his irritating play goaded the Ottawa winger into an unprovoked fight.

The Stars capitalized as Jokinen drew a hooking penalty to give the Stars a 5-on-3, and Dallas scored quickly. Sergei Zubov's shot on net was deflected by Brenden Morrow, and the rebound of that shot came out to Hagman, who was able to shovel in his 11th goal of the season.

That goal was sandwiched by two Ottawa goals and plenty of penalty kill time for the Stars. Dallas finally broke down in the third when Mike Fisher swept in a shot from the left circle.

"I needed to make some saves early, and I didn't do it," Smith said. "Once you get behind, you're chasing the game."

Tippett said there was plenty of blame to share.

"A couple more saves would've been nice," he said. "But we need to find a way to score more ourselves."