The struggling Senators saw Montreal winger Erik Cole score three goals in the first 5:41 of play as the Canadiens skated to a 5-1 victory on Friday night.
A third loss in a row left seventh-place Ottawa (37-28-10) only two points up on both eighth-place Washington, who lost in overtime to Winnipeg, and ninth-place Buffalo, which beat the New York Rangers 4-1. All three teams have seven regular season games left to play.
And now the Senators face the red-hot Pittsburgh Penguins back in Ottawa on Saturday night.
"Pressure's a wonderful thing," said Senators head coach Paul MacLean. "You can find out a lot about yourself and about your team, and how hard it is the league.
"For some reason we feel we have that on us and we have to find a way to handle it or channel it into the right spots."
Cole set a Canadiens record for the quickest hat trick from the start of a game.
Petteri Nokelainen also scored in the first and Lars Eller added one in the third for Montreal, which is 4-1-3 in its last eight. The Canadiens (29-33-13) playoff hopes have been all-but mathematically dashed for a couple of weeks.
"Something was mentioned to me (about the record), but it's not really in the forefront of my mind right now," said Cole, who matched a career high of 30 goals for the season.
The Canadiens only role at this point is to play spoiler, and they've done that with Ottawa, going 4-0-2 against their closest geographic rival this season.
"I'm glad we don't play them anymore," added MacLean. "They certainly bring the worst out in us and tonight we weren't as prepared to play the game and we didn't play with enough discipline."
Montreal coach Randy Cunneyworth said his team goes into games with the Senators worried about their offensive firepower and "that fear is what brings out your best. All year we've played our best against the best teams."
Everything went wrong for Ottawa in this game.
Goaltender Craig Anderson returned after missing 12 games from slicing a finger in a kitchen accident and allowed two goals on four shots before he was replaced at the 4:56 mark by Ben Bishop, who gave up two on nine shots. Anderson went back in to start the second frame.
Playing catch-up, the Senators stepped up their physical play and that led to penalties. Montreal went 2-for-7 with the man advantage, while Ottawa's power play went 0-for-2 to leave it 0-for-23 in recent games.
Ottawa has scored only six goals in its last five games.
"You look at the last for or five games, our discipline hasn't been great," said Ottawa defenceman Chris Phillips. "We're spending a lot of time in the penalty box.
"Whether right or wrong, it doesn't matter. You can't expect to be successful when you're doing that. We need a stronger focus on just playing the game, playing it hard."
It doesn't get easier for Ottawa the rest of the way, starting with a three-game road trip beginning Monday night in Winnipeg followed by games in Philadelphia and Long Island.
"The rest of the stretch, they're all pretty much playoff games," said centre Jason Spezza. "Teams are chasing us and getting wins and we're not right now. So they're all must-win. We just have to put this behind us and admit that we played bad."
Spezza, playing his 600th career game, scored Ottawa's goal. It gave the 28-year-old 30 goals for a fourth time in his career and the first time since 2008-09.
Ottawa outshot Montreal 38-32 in a chippy, nearly three-hour-long game that had three goal reviews and frequent skirmishes after whistles.
Cole scored on the first shot on Anderson, who saw a routine shot go off his glove and into the net only 29 seconds in. Cole put in the rebound of P.K. Subban's shot at 4:56 to chase Anderson.
Cole was on the doorstep to slip in a Subban shot that got behind Bishop at 5:41.
Nokelainen beat Bishop from the left circle at 8:21, but Spezza got his team back after Milan Michalek did good work to feed him in front to beat Carey Price with 13 seconds left in the period.
Eller got Montreal's second power-play goal of the game when his bad-angled shot went in under the cross-bar 5:05 into the third.
The bad start was likely the difference for Ottawa, but there was also a 37-save effort from a very sharp Price.
"Those things happen and we have to have the focus to not let those things affect us," Phillips said of the early goals. "No matter what happens in any game, to continue to play our game and not get distracted, lose our focus and take it out on other factors.
"Instead, we need to put it where it needs to be, which is obviously turning our game around right now."
Montreal defenceman Yannick Weber left after the first period with a lower body injury.
The overall record for fastest hat trick is 21 seconds by Bill Mosienko on March 23, 1952. The Canadiens record for a fastest hat trick was 44 seconds by Jean Beliveau set in the second period of a game on Nov. 5, 1955.
Notes: Bishop had made the last seven straight starts for Ottawa. Alex Auld didn't dress. . . Spezza's return after missing a game with an illness bumped Bobby Butler from the lineup, while Kaspars Daugavins and Matt Carker didn't dress. . . Spezza has 608 points in 600 games. . . Erik Condra played his 100th game. . . Blake Geoffrion didn't play for Montreal.