Hamrlik scored Montreal's first goal in 10 days 12:56 in to end a 199-minute, 1-second scoring drought.
"Usually I'm on the blue line but I just skated behind the net and the puck was bouncing right there," the Canadiens' veteran defenseman said. "It was just a lucky bounce for me."
That goal had not even been announced when Darche made it 2-0 at 13:07, to the delight of the sold-out crowd of 21,273.
"Obviously it's a big monkey off everybody's back when we popped that first one," said Carey Price, who made 27 saves.
Price lost a shutout bid 8:35 into the third on a controversial goal by Nik Antropov. Canadiens defenseman Hal Gill was cut near his right eye when he was struck by Eric Boulton's stick on the play that led to Antropov's tally, which drew Atlanta within 2-1. No penalty was called.
"We all froze for half a second," Price said. "Maybe we expected something but things happened so fast."
Andrei Kostitsyn scored into an empty net with 1:20 remaining.
Price had allowed eight goals and been pulled once during the Canadiens' three-game losing streak, during which Montreal was outscored 11-0 while enduring three straight blank sheets for the first time in over 61 years.
The Canadiens are sixth in the Eastern Conference with 89 points, two ahead of the New York Rangers.
Ondrej Pavelec stopped 28 shots for Atlanta, which is 11th in the East with 76 points. The Thrashers, who have six games remaining, are nine points behind the Buffalo Sabres for the eighth and final playoff spot.
The task at hand is clear.
"It's 6-0, that's the reality of it," Atlanta defenseman Ron Hainsey said. "It may have been 7-0, this may have been a must-win, too. The goal is to win every game the rest of the way and see where that takes us."
The frustration continued early as Pavelec stopped Mike Cammalleri on a breakaway 7:11 in and Montreal defenseman James Wisniewski's slap shot hit the left post at the end of a power-play opportunity midway through the opening period.
Hamrlik finally delivered the Canadiens' first goal in four games when he crashed the crease to put home his own rebound 12:56 in.
"Wiz gave me a nice pass in the slot and I should have scored from that shot but the rebound was there," Hamrlik said. "It's nice to score. I don't score too many goals so it's always nice, and we're happy we got two points."
Montreal was shut out in four straight games in February 1928.
Darche made it a 2-0 lead 11 seconds later when he beat Pavelec from the goal mouth with a quick shot off Scott Gomez's feed from behind the net.
Boulton cut Gill on the corner of his right eye with a high stick on the play that led to Antropov's goal 8:35 into the third.
Antropov left the puck for Boulton inside the Canadiens blue line and crossed over to the middle of the ice. Boulton's stick came up and cut Gill as he played the puck, and the Thrashers forward carried on toward the net while the Montreal defenseman scrambled to follow while putting his glove to his bloodied face.
"When you get a stick in the eye it's tough, so sometimes you react to that," said Gill, who had a cut on his right eyelid.
Boulton passed to Antropov, who tucked the puck past Price to draw Atlanta within one.
"No whistle, you just play to the end and fortunately for us we scored," said Antropov, who didn't see Boulton's stick strike Gill.
Referee Bill McCreary, who was given a warm ovation from the Bell Centre crowd just before the opening faceoff when it was announced that he was calling his final game in Montreal, conferred with the other on-ice officials, though ultimately the goal stood and no penalty was assessed.
"They said they missed it," Gill said. "Luckily it wasn't a big miss. It could have been a tough one but those things happen. He missed it, what are you going to do?"
Thrashers right winger Chris Thorburn fought with Montreal's Travis Moen late in the first. ... Boulton got a misconduct penalty when teammate Zach Bogosian was called for crosschecking 13:52 into the second. ... Gill was among the Canadiens players who shook hands with McCreary at the end of the game. "He's been around forever so it's too bad we have to see him go," Gill said.