"We always seem to ease off the gas a little in the second period and help them keep it a game," Toews said. "It's one of the things we need to do better."
In their last five games, the Blackhawks have been outscored 7-0 in the second period. In their last 10, they've been outscored 11-5 in the middle frame.
"If we get easy goals in the first period, maybe we're thinking the game's already over," Toews said.
Chicago's Dave Bolland scored early in the third period to get the game to overtime. The Blackhawks peppered Atlanta goalie Ondrej Pavelec with 14 shots in the third period and four more in overtime before Toews finally got one past him in the first round of the shootout.
Hossa scored his NHL-leading fifth short-handed goal, but was shouldered in the head by Atlanta's Colby Armstrong in the third period and is listed as day-to-day. Chicago plays at Columbus on Sunday before the Olympic break, and Hossa is scheduled to skate for Slovakia in the Vancouver Games.
Chicago coach Joel Quenneville said Hossa "was doubtful" for Sunday's game.
Johnsson, a defenseman, connected in his first game with the Blackhawks. He was acquired Friday along with Nick Leddy in a deal that sent Cam Barker to Minnesota.
"It was a game where you had a false lead, that it was going to be easy. That there would be offense without needing to check," Quenneville said. "The game got turned around. We were fortunate to come out with two points."
Pavelec stopped 36 shots through overtime, and was sharp late in the game to force the shootout.
"I think it was a good point against a great team," Pavelec said. "We started slow a little bit in the first period, but we came back and scored three goals in the second period.
"I was a little lucky there in the third a few times, but in the last three games we got four points and it's pretty good."
Chicago rookie backup goalie Antti Niemi made 23 saves, but allowed soft goals to Slater and Afinogenov.
The crowd of 22,275 was the Blackhawks' largest this season and their 81st straight sellout. ... Atlanta played its final game before the Olympic break. Five Thrashers will compete in the Olympic Games Pavelec and D Pavel Kubina (Czech Republic), D Enstrom and D Johnny Oduya (Sweden), and RW Afinogenov (Russia). ... Six Blackhawks will head to Vancouver D Duncan Keith, D Brent Seabrook and Toews (Canada), RW Patrick Kane (U.S.) and RW Hossa and RW Tomas Kopecky (Slovakia). ... Chicago C John Madden missed the game with a lower-body injury and is expected to return following the Olympic break. Blackhawks LW Ben Eager missed his third game with a lower-body injury ... Atlanta D Mark Popovic sat out his second game with upper-body injury.
Copyright by STATS LLC and The Associated Press
CHICAGO - FEBRUARY 13: Kim Johnsson #8 of the Chicago Blackhawks skates during warm-ups before his first...