Lack replaced an injured Roberto Luongo late in the first period then watched defenceman Chris Tanev score the winning goal midway through the third as the Vancouver Canucks defeated the Jets 2-1 in a tight NHL game.
"I was a bit surprised for sure," said Lack, who stopped 15 shots to improve his record to 6-2-0. "I didn't hear anything before that he was hurt.
"I just stuck my glove on and got out there."
Luongo, one of the goalies being considered to represent Canada at the 2014 Sochi Olympic Games, suddenly left the ice with 3:30 remaining in the first period.
Head coach John Tortorella said Luongo had a lower body injury and is day-to-day. The game was Vancouver's last before the Christmas break and the Canucks don't play again until Dec. 29 in Calgary.
Luongo had his leg clipped early in the period by big Winnipeg defenceman Dustin Byfuglien. He also was knocked flat on the ice during a goal-mouth collision with the Jets' Blake Wheeler.
Tortorella said Luongo had spoken with trainer Mike Burnstein briefly a couple of shifts earlier but had no idea the veteran goaltender was in any trouble.
"I didn't know," he said. "It surprised me."
Tanev broke a 1-1 tie at 10:23 of final period when he took a pass in the high slot from Zack Kassian and ripped a shot past Winnipeg goaltender Ondrej Pavelec. It was Tanev's fourth goal of the season, leaving him tied among Canuck defenceman with Dan Hamhuis and Jason Garrison.
"I'm just trying to get pucks to the net," he said. "It seemed like the seas parted when I got it. It was awesome when I walked into it."
Brad Richardson also scored for Vancouver with his first power play goal of the season.
Tortorella said the Canucks need players like Tanev and Richardson to contribute as the season continues.
"You can't depend on just a couple of guys," he said. "I don't think this team for the last little while has.
"I think everybody has kind of chipped in."
Evander Kane scored on the power play for Winnipeg.
The Jets pushed Canucks at times but couldn't beat Lack. Winnipeg has lost five of its last seven games.
"We had some opportunities to score but I thought we didn't push the pace that we needed to," said Kane.
"Not having the success now, it's very frustrating. It's not something you want to be part of. We're going to have to figure out a way to change that and get out of that rut."
The Canucks came into the game riding the emotion of a 3-2 shootout victory over the Blackhawks Friday night in Chicago. Lack was in goal for the game that saw Vancouver battle back from a 2-0 deficit.
"It's fun when the team is winning," said the 25-year-old Swede, playing in his first season with the Canucks. "I feel like I have a great connection with the team.
"I feel like they are there for me. It makes it easier."
The win was even sweeter for Lack since his father, grandmother and girlfriend were among the sellout crowd of 18,910.
Tortorella praised his team's effort, especially coming off a three-game road trip.
"At the beginning of the third period it looked like we were ready to drop," said Tortorella. "I really respect the way they held on."
Winnipeg coach Claude Noel said his team failed to take advantage of its chances.
"I thought we carried a fair bit of the play, but there's a difference between carrying the play and finishing your plays," he said. "It isn't about scoring chances.
"We just couldn't close out the game. That was the disappointing part."
Richardson opened the scoring at 10:09 of the first period when he deflected a Hamhuis shot past Pavelec.
The Jets tied the game at 9:38 of the second period. Wheeler sent a pretty pass to Kane, who beat Lack on the glove side. Jets rookie Mark Scheifele earned an assist for his eighth point (three goals, five assists) in the last five games.
The goal came just a few minutes after Lack made a big stop off a point-blank shot from Byfuglien.
Referee Ian Walsh left the game in the second period after a collision with Vancouver's Dale Weise. The game continued with Kyle Rehman acting as the lone referee.
The Canucks improved their record to 22-11-6 for 50 points, leaving them tied with the San Jose Sharks for fifth-place in the Western Conference. The Jets are 11th in the West with a 16-17-5 record for 37 points.
The Canucks have won nine of their last 11 games and collected points in 10 of those matches.
CANUCK NOTES _ David Booth's assist on Tanev's goal was his 100th career assist. ...Defenceman Kevin Bieksa played his 500th career game. ....Vancouver's Tom Sestito and Winnipeg's Anthony Peluso engaged in a first-period fight.