Senators defenseman Sergei Gonchar is mobbed by teammates after putting the game-winning goal past Michal Neuvirth. (Jonathan Newton/The Washington Post)

Although the Washington Capitals clinched a postseason berth earlier this week, Coach Adam Oates’s message remained consistent: Stay the course. He doesn’t want to see the Capitals develop bad habits or risk going into the playoffs on a slide.

But for the first time in months the outcome of a game meant far more to the opponents than to the Capitals, and that discrepancy was visible late Thursday night at Verizon Center as the Ottawa Senators pressed for a critical two points.

Ottawa clinched a playoff spot 47 seconds into overtime when former Capital Sergei Gonchar scored to give the Senators a 2-1 victory. Both of Washington’s losses in the past 10 games have come against the Senators.

The Senators’ desperation to secure their postseason berth was readily apparent in the third period and overtime as they outshot Washington, 25-4, in those 20-plus minutes of play.

“They came to play tonight. They skate hard and they skate fast, they’re on us and they put the pressure on and it’s tough to create anything,” Capitals defenseman Mike Green said. “But we just came out flat. I don’t know what it is the last couple times we’ve played against them. But it’s the way it’s gone.”

The Capitals defeated the Jets on Tuesday to clinch their fifth Southeast Division in six years. (Travis Swain for Synthesis/Koubaroulis LLC./The Washington Post)

While the Capitals certainly weren’t playing with the same stakes as their foes, the contest picked up in intensity during the game’s second half as the two teams offered a preview of what a first-round playoff series might look like if they’re matched up against each other at the conclusion of the regular season.

Washington could still face any one of four teams — Ottawa, Toronto, the New York Islanders or New York Rangers — in the Eastern Conference quarterfinals next week.

The Senators are the only team in that group that Washington hasn’t defeated in the regular season and part of what makes them a frustrating matchup is their patience and willingness to simply protect goaltender Craig Anderson, who leads the league in goals against average and save percentage and finished with 19 saves Thursday night.

“They don’t give you much. They’re willing to wait and wait and wait. We had to do the same thing,” Oates said. “It makes it very frustrating. They have a very good goalie and they protect him they don’t give you much. They’re a pretty disciplined team. They wait for their opportunities and you have to kind of match that when you play them.”

For the first 30 minutes the teams traded occasional chances and the Capitals matched Ottawa in the waiting game. Anderson made a few quality stops as did Michal Neuvirth, who finished with 39 saves in just his fifth start in 36 games.

With 12:35 gone in the second period Ottawa defenseman Erik Karlsson, who was playing in his first game since suffering a lacerated left Achilles’ tendon on Feb. 13, helped tip the balance in Ottawa’s favor.

Karlsson had hopped onto the ice and immediately began tapping his stick, requesting the puck. Milan Michalek, who was working his way out from behind the net, obliged the reigning Norris Trophy winner and Karlsson let go a long-range shot from the point. Rookie winger Jakob Silfverberg deflected the shot on its way to the net, sending it past Neuvirth for a 1-0 lead that seemed like it might be enough for Ottawa to secure a victory.

The start of the third period brought flaring tempers and plenty of altercations both large and small between the whistles. It seemed as though any stoppage around either net yielded extracurricular activities.

At the 5:33 mark of the frame Martin Erat pushed Ottawa’s Daniel Alfredsson into John Erskine, who was right next to the net. Erskine then pursued Alfredsson, prompting every Senator on the ice to come to the aid of their captain and creating a ruckus that resulted in both defenseman and center in the box for roughing.

“I think that’s kind of playoff hockey,” Erskine said. “Low-scoring, tight-checking, always little things going on after the whistle, little bumps.”

Alex Ovechkin put the Capitals on the board with his 32nd goal of the season, tying the contest at 1 on the home team’s first shot of the third period with 8:31 elapsed. Marcus Johansson carried the puck up ice and lobbed a bouncing puck over the stick of Senators defenseman Chris Phillips, giving Ovechkin a step on the veteran blue-liner. Ovechkin gained possession, blazed past Phillips down the right wing, cut to the net and then tucked the puck around the outstretched leg of Anderson.

A fracas broke out in the final minute of regulation earning Mike Ribeiro a roughing minor and a 10-minute misconduct for Jason Chimera, who wasn’t even on the ice but apparently voiced his displeasure from the bench. Ribeiro’s penalty proved to be costly as it was on the resulting power play, which extended into overtime, that Gonchar scored on. The veteran defenseman fired a blast from the point for the gamewinner just 47 seconds into extra time.

Even though he recorded the Capitals’ only goal, Ovechkin didn’t feel as though he and his teammates made the most of their opportunities against Ottawa and hopes they learn from the lesson.

“I think we’re getting to the zone but, if we stay there maybe 10 times we have only three or four shots. We have to create more chances out there, especially against that kind of team. We don’t use D a lot today, tomorrow probably going to watch the game, see what’s happening and we have to do better next time.