Butler got his third point of the game with an assist on Filip Kuba's goal 1:16 into overtime that gave Ottawa a 3-2 victory over the Montreal Canadiens on Thursday.
Kuba won it in the extra period with a drive from the point that got past the Canadiens' backup goalie.
"It's definitely a great feeling to get two points in overtime," said Butler, who gave the Senators a 2-1 lead with his ninth goal 17:11 into the third. "It was a great game, a lot of excitement in the stands, which is awesome, and it just feels great to get the win."
Anderson made 26 saves for Ottawa, 13th in the Eastern Conference with 74 points. The Senators had made the playoffs 12 of the 13 previous seasons, including 11 in a row from 1997 to 2008.
"The fans have been great," said Jason Spezza, who had a goal and an assist. "We've been out of it here for a little bit and they've kept showing up and giving great support, and it hasn't gone unnoticed in the dressing room. We've wanted to play hard to show them that we're a better team than our record is and we're going to be better next year."
Brian Gionta scored his team-leading 27th goal for Montreal, which fell short in its first attempt to give coach Jacques Martin his 600th career win. The Canadiens clinched their fourth straight trip to the playoffs with a 2-1 overtime win over Chicago on Tuesday night.
"I think that we've been playing very well lately and we had a real playoff game against the Blackhawks on Tuesday and last Saturday in New Jersey," Martin said. "Tonight we weren't as good and we didn't win so you hope to learn from those experiences."
Auld stopped 29 shots in his first game of the season against his former team.
"It's a challenge, obviously, clinching the other night and then playing against a team that's not in playoff mode," Auld said. "They're a little freer, a little looser, playing for jobs for next year."
Butler assisted on Spezza's tying goal early in the third. Spezza tied it a 1 with his fourth goal in three games when he put away a rebound 36 seconds into the third. He drew an assist for his eighth point in three games when Butler snapped a wrist shot past Auld to give Ottawa its first lead with 2:49 left in regulation.
A short-handed chance by Ottawa's Brian Lee was the best scoring opportunity on the ensuing 5-minute power play. The Canadiens were held without a shot until Anderson stopped Paul Mara's drive from the point with a second left in the major to Lessard.
Canadiens defenseman Jaroslav Spacek returned after missing 23 games because of a knee injury that required surgery.
Gionta scored 13:13 into the second when he put James Wisniewksi's rebound into an open left side before Anderson could lunge across. The Montreal captain put a shot off the left post with three minutes left in the second.
- A moment of silence was observed prior to the game in memory of E.J. McGuire, the NHL's head of central scouting. McGuire died of cancer Thursday at the age of 58. He was an assistant coach for the Senators' first three seasons from 1992-95.
- Anderson is the fifth Senators goalie Montreal has faced this season.
- The crowd of 19,809 was Ottawa's 16th sellout.