Dominik Kahun scored in his debut with the Sabres (29-27-8), who have lost two in a row and remained 10 points behind the Columbus Blue Jackets for the second wild card into the Stanley Cup Playoffs from the Eastern Conference. Carter Hutton made 24 saves.
"We played them eye to eye for 40 minutes, but that's not enough," Sabres coach Ralph Krueger said. "You've got to play them 60 minutes. We didn't do it and we need to learn to do that. We learn from pain and this is a lot of pain right now."
Kahun, who was acquired in a trade with the Pittsburgh Penguins on Monday, scored on his first shift with Buffalo to make it 1-0 at 2:16 of the first period.
"You just look at the next shot and just try to make the next save," said Lehner, who stopped his next 32 shots. "I thought we got better as the game went on, and obviously had a great jump in the third and got a couple of goals to settle it down."