Francis Bouillon scored 1:26 into overtime as the Canadiens erased a three-goal deficit in the third period and rallied to defeat the Senators 5-4 on Saturday night.
David Desharnais tied it for Montreal with 1 second left in regulation for the Canadiens, who trailed 4-1 five minutes into the final period.
"I don't really know what to say," said Marc Methot, who was on the ice for Ottawa on the tying goal. "It felt like we were in control, even in the third period. We weren't playing on our heels, at least for a good amount of it.
"They got confidence, and they got the crowd back into it."
Bouillon made for an unlikely overtime hero as he entered the game with no goals in 40 games this season.
Eller got the comeback started for Montreal, scoring at 16:38 of the third to reduce the deficit to two. Eller pushed a rebound past a sprawled-out Lehner for his first goal in his last 25 games.
Gionta, who assisted on Eller's goal, added a score of his own less than minute later as he deflected P.K. Subban's shot to the back of the net to make it 4-3.
With the Canadiens on the power play and their net empty for the extra attacker, Montreal sent everybody to the front of Lehner's net and Desharnais put in the tying goal at 19:59 off a feed from Subban.
"I looked up at the clock to see how much time there was," Subban said. "I saw quickly that there were 4 seconds left. If I had the shot, I'm sure it would have been blocked. I saw Davey (Desharnais) waving at me.
"Big players score in those big moments."
The comeback wasn't without controversy, though. On the winning goal, Senators players were convinced Lehner had frozen the puck long before it was poked away by Max Pacioretty onto Bouillon's stick.
After the game, referees apparently told Ottawa captain Jason Spezza that there was no whistle on the play because the building was too loud.
"I have no idea what that means," Senators coach Paul MacLean said. "That's the explanation we got. I'm confused."
Added Methot: "I'm pretty frustrated. It was almost deafening toward the end when they scored. I have to be careful with the words I use. It looked like our goalie had possession of the puck. It's tough for the refs, I get that. There's a lot of noise, a lot of distractions."
The game marked the return of Price, who saw his first NHL action since Feb. 8, before the Olympic break. Price was out of the lineup for eight games with a lower-body injury that he sustained in Sochi.
The 26-year-old Price made 29 saves for his 27th win. After the game, however, coach Michel Therrien announced that Price would not travel with the team to Buffalo for their next game, presumably due to the injury.
The Canadiens came out flying, putting one past Lehner on their third shot, 38 seconds into the first period. Following Tomas Plekanec's faceoff win, Briere took advantage of laid-back defending by Erik Karlsson to walk to the front of the net and fire home his 12th of the season.
Spezza tied it on the Senators' first shot of the game at 3:08, beating Price with a rocket of a slap shot into the top corner of the net.
The Canadiens outshot the Senators 17-4 in the first period.
Minutes after seeing one of its goals disallowed, Ottawa took a 2-1 lead at 17:10 of the second period when Smith scored on a breakaway.
Hemsky doubled the lead at 1:54 of the third, beating Price under the blocker for his seventh point in four games since being traded to the Senators. MacArthur made it 4-1 three minutes later.
Eller scored his first goal in his last 25 games at 16:38. Gionta added another less than minute later before Desharnais tied it.
Lehner got the start for Ottawa in place of starter Craig Anderson (shoulder), who was injured in the third period of Monday's loss to the Nashville Predators. ... Michael Bournival (concussion) missed his 10th consecutive game. ... Ottawa wore their heritage jerseys. ... Thomas Vanek has yet to score on 13 shots in four games since donning a Canadiens uniform. ... The last time the Canadiens and Senators met, on Jan. 16, Subban was criticized for celebrating his overtime-winner with gusto. The teams play once more this season, on April 4 in Ottawa.