More than anything else, Lehtonen was angry that the injury gave Buffalo the split-second needed to tie the score in the third period.
"I was out for just enough time for them to score," Lehtonen said. "It was a lucky bounce for them. We didn't get the rebound, and they scored right away."
Keith Tkachuk's power-play goal with 38 seconds left in overtime gave Atlanta a 4-3 victory over the Sabres on Sunday and extended the Thrashers' home winning streak to seven.
Atlanta has 88 points and leads Tampa Bay by six in the Southeast Division. The Lightning lost 7-1 at Washington.
Buffalo, the best team in the Eastern Conference, had won two straight. The Sabres clinched a playoff spot following Toronto's shootout loss to Montreal on Saturday.
Since the Thrashers traded for them in late February, Tkachuk and defenceman Alexei Zhitnik have helped Atlanta go 8-2. Zhitnik's seventh goal, coming on a power-play slap shot midway through the third, gave the Thrashers a 3-2 lead.
Buffalo tied it 3-3 on Derek Roy's 15th goal with 7:35 remaining. Lehtonen managed to stay upright after the puck hit his mask, but he fell face first to the ice after Roy lifted a wrist shot over his shoulder from the bottom of the left circle.
Lehtonen, who improved to 32-21-8, stayed in the game after a trainer attended to him. He stopped 35 of 38 shots, including four in overtime, one of them a glove save to help kill a slashing penalty on Tkachuk.
It was Henrik Tallinder's slap shot from the left circle that injured Lehtonen and bounced to the rear boards. Roy quickly gained control and scored.
"It was the best game we played on the trip," said Sabres coach Lindy Ruff, whose team went 2-2 away from Buffalo. "If you look at it from the chances we created and the ones we gave up, we didn't give up much tonight. We generated quite a few. We had opportunities to win it, but we missed on some great opportunities."
Jaroslav Spacek committed the same mistake, a holding penalty in overtime, that Matt Cullen made for the New York Rangers on Friday night.
"It's tough to penalty kill in that situation," Sabres goalie Ryan Miller. "We worked hard, but we didn't quite click. We needed to stay out of the box."
Tkachuk scored his 26th goal, his sixth with the Thrashers. Zhitnik, who had the game-winner in overtime against the Rangers, assisted on Tkachuk's goal.
"We found a way to win, and that is what you need," Tkachuk said. "Obviously, our power plays are clicking right now. This is what wins and loses hockey games."
Ilya Kovalchuk's 38th goal, on a two-man advantage early in the first period, gave Atlanta a 1-0 lead. Drew Stafford responded for Buffalo with his ninth goal at the 6:11 mark of the period.
Eric Belanger put the Thrashers up 2-1 on a breakaway 15:36 into the first, but Thomas Vanek's 35th goal made it 2-2 early in the second.
Atlanta coach Bob Hartley believes Lehtonen, despite the ear injury, is showing the benefits of the 15-game stretch of consecutive starts that ended on Feb. 10 with a 3-2 loss at Vancouver. Lehtonen went 6-7-2 during that long run.
"That was on purpose," Hartley said. "It was to make sure he got the message that he was our guy, and it's not to take anything away from (No. 2 goalie Johan Hedberg). But at the same time, he's never done it at the NHL level. You have to go through this once in your career to know what it takes."
Notes: Thrashers defenceman Greg de Vries didn't return after leaving the game and walking to the locker room with an undisclosed injury with 14:48 remaining in regulation. No player on either team interfered with de Vries, who collapsed but stood up before a trainer approached him near the left boards. ... Roy had his 37th assist and Vanek his 34th on Stafford's goal. ... During the past 14 games, the Thrashers have killed 56 of their past 62 penalties, including a double-minor on Kovalchuk that carried into the first 3:16 of the second. ... After earning an assist on Kovalchuk's goal, Marian Hossa earned his 53rd assist when Tkachuk scored. Over his past 14 games, Hossa has 21 points.