"Good first, bad second, good third," he said.
Lehner made 21 of his 35 saves in the second period, and Milan Michalek and Erik Karlsson scored as Ottawa snapped a three-game skid.
"We went from having one of our best periods in the first to just a terrible second period," said Kyle Turris, who had an assist in the win. "(Lehner) stood on his head and kept us in it. We can't let that happen."
Ottawa managed just four shots in a turnover-abundant second period, but Lehner withstood Buffalo's best attack. He was aided when Mike Weber's goal was disallowed due to incidental goaltender interference from Marcus Foligno.
"I couldn't take ice," Lehner said. "He stood right in front. I had my skate on the post and still his pants were right in my face."
Tyler Myers scored Buffalo's goal as the Sabres dropped to 1-8 in their past nine home games. Buffalo has the fewest standings points in the NHL with 35.
The Sabres beat Lehner on a third-period power play. With Eric Gryba in the box for elbowing, Myers' point shot found its way through a maze of bodies and past a screened Lehner at 5:08.
"If we keep playing like we did in the second and third I think we'll be rewarded," Myers said. "Our first period was not very good at all. We didn't look engaged."
The tie was broken as Jhonas Enroth gave up a big rebound on Patrick Wiercoch's shot and Michalek slapped it into the goal.
Tyler Ennis rang a wrist shot off the crossbar in a good late chance for the Sabres.
"A few breaks today and that's nice," Lehner said. "Haven't seen those in a while. Feels good."
Ottawa's first sustained pressure came five minutes into the game, and Sabres defenceman Josh Gorges batted an airborne puck out of danger as it reached the goal line.
The Sabres received Bronx cheers midway through the period when Zemgus Girgensons' shot was caught by Lehner for Buffalo's second shot of the game and first since the opening moments.
"I just felt the first period, the first 10 minutes particularly, we weren't in the play at all," Sabres coach Ted Nolan said. "We weren't skating. We weren't working, winning the battles."
A tripping penalty against Brian Gionta gave Ottawa the first power play of the game, and the Senators wasted little time converting the chance.
Karlsson's slap shot from the point took a turn off Girgensons' stick and beat Enroth to give the Senators at 1-0 lead at 12:18 of the first.
"We had real good jump in the first and Buffalo was a little bit flat," Ottawa coach Dave Cameron said.
Weber slid a pass to give Ennis a shot on Lehner late in the period, and then had a shot stopped by the Senators' goalie at 16:34.
Lehner made a save on Patrick Kaleta early in the second period, catching the puck with the inside of his blocker pad. He then made a point-blank save on Nikita Zadorov as the Sabres took the first 15 shots of the period.
Buffalo nearly tied it on shot No. 14, when Myers' deflected shot skittered to a stop inside the right post before being cleared away. Then came Weber's disallowed goal.
Buffalo's 21 second-period shots were a season high, and the Senators had a contentious talk in the locker room.
"The message was loud and clear," Mark Borowiecki said. "We just weren't hard enough. We didn't stick to our game plan."
NOTES: Sabres C Cody Hodgson missed his second straight game as a healthy scratch. ... Lehner made his sixth straight start for Ottawa. Backup Andrew Hammond has not played for the Senators this season.