MONTREAL -- The Montreal Canadiens achieved their goal of returning to the playoffs ahead of schedule.
Chris Higgins also scored in the first as Montreal beat Martin Gerber three times in the opening period while outshooting Ottawa 14-7.
Carey Price stopped 31 shots for Montreal, which returned to the playoffs for just the fourth time in the past nine seasons.
"It's a big credit for all the players here," Bouillon said. "It's a big surprise -- nobody was expecting that from the beginning of the season and we worked pretty hard all season long to be there. Tonight was a great victory for us."
The Canadiens, who were eliminated from playoff contention last season with a loss in Toronto in their final regular-season game, lead the Eastern Conference with 96 points and five games remaining.
"It gives us some time to get ready for the playoffs and obviously we have games still left and we want to finish first," captain Saku Koivu said. "That's our goal now, but it's kind of a derivative from preparation when you know that you're going to be there than a lot of years before where we played to the last game and still didn't know if we were going to make it or not."
Montreal, which has a three-point lead over Pittsburgh atop the conference, also extended its Northeast Division lead to seven points over Ottawa, which has six games remaining, including Tuesday night in Buffalo.
"We've still got some games left," said Jason Spezza, who scored with 1:58 remaining to draw the Senators within two. "If we win five of the next six then we'll have some momentum going in. It all depends how you look at it but we know we have to get better, and we know we can't give up early goals to teams. It's no time to panic, we just have to get things going a little bit."
Dany Heatley got his 38th and 39th goals for the Senators, who scored four times in the third period after falling behind 7-1 late in the second.
"We kind of got a little settled down and too relaxed and they really picked up their game," said Kostopoulos, whose short-handed goal with 46 seconds left in the second put Montreal up by six. "The combination of the two led to a strong third period for them and a weak one for us but we were fortunate that we had a big enough lead to hold onto the game."
Kostitsyn opened the scoring 1:40 in with his 24th goal. Higgins made it 2-0 at 13:26 when he put his own rebound past Gerber, who was unable to cover the puck.
Kostitsyn got his second goal of the period -- his 25th of the season -- on a power play at 18:24 as Gerber once again was unable to smother a puck in his crease.
"Goaltending has been solid for us," said Senators captain Daniel Alfredsson, who assisted on three of Ottawa's four third-period goals. "Marty has been really consistent for a two-week period. I don't see that as the issue, it's more the breakdowns we have defensively. When we play well and move the puck, we're really good, but it's those easy goals that we give up and come playoff time, those are tough to overcome."
Emery took over to begin the second and fared no better than Gerber, even after Vermette scored his 19th goal midway through the period to draw Ottawa within 3-1.
Bouillon scored his second of the season at 11:29 to restore Montreal's three-goal lead before Markov and Grabovski scored goals 42 seconds apart to make it 6-1 at 15:46.
Kostopoulos increased the lead to 7-1 when he got the Canadiens' fourth goal within 7:45 on a short-handed effort at 19:14.
Heatley, a 50-goal scorer the past two seasons, got his 38th goal 3:04 into the third to cut the lead to 7-2 and Lapointe made it 7-3 with his sixth of the season, his third in 12 games since he was traded to Ottawa by Chicago at the deadline.
Heatley got his second goal in just over 6 minutes when he beat Price for his team-leading 39th goal at 9:04 to draw the Senators within 7-4.
Spezza scored a power-play goal at 18:02 to cut the lead to two.
- Gerber made his 11th straight start.
- With centers Chris Kelly and Dean McAmmond out of the Senators' lineup, RW Brian McGrattan dressed for the first time in seven games. McGrattan, who had 5:42 total ice time in the game, had been a healthy scratch for 11 of 12 games since Feb. 25, when he dressed for a 5-0 loss to Toronto but did not appear in the game.
- Canadiens LW Guillaume Latendresse missed his second straight game because of a neck injury. He is day to day.