BOSTON -- Michael Ryder kept it simple in the shootout.
It was the fifth win in six games -- and sixth straight over the past two seasons against Ottawa -- for the Bruins, who moved into first place in the Northeast Division after an injury-filled, sluggish start this season.
After the first six attempts were stopped in the shootout, Ryder just went onto the ice and went with felt best.
"I feel like I think too much, maybe that was the difference," Ryder said. "I just went on instinct. I really didn't know what I was going to do going in on him."
He was just 2-for-14 in his career and 0-for-2 this season before the winner.
"He's been working on it in practice and he's getting better," Boston coach Claude Julien said. "Maybe he didn't have too many shootout chances early in his career."
Ottawa's Milan Michalek forced overtime, scoring his second goal of the game with 19.3 seconds left and the goalie off for an extra attacker.
"I thought we got off to a real good start, almost too good, too soon, then we sort of just got very lethargic in the middle frame of that game," Ottawa coach Cory Clouston said. "I thought the last part of the second part and a good portion of the third period we were OK, but we didn't do enough good things."
Daniel Alfredsson scored a goal, set up another and made an outstanding goal-saving defensive play for Ottawa.
The Senators lost just their second in their last six games.
Thomas, starting after missing the previous six games with an undisclosed injury, made 19 saves before the shootout. He gave up a goal on the first shot he faced and was showered with a mock cheer when he made an easy glove save after falling behind 2-0.
"I messed up. I had to tell the guys on the ice that I messed up," Thomas said.
It was the Bruins' third straight shootout game, with them splitting the other two.
Elliott stopped 30 shots.
Wideman sent a wrist shot from the middle of the blue line that found its way through a crowd of players and over Elliott's right shoulder to give the Bruins a 3-2 lead midway into the third period, but Michalek slipped a wrist shot by Thomas from in close to send it to overtime.
"We had to battle back and get some positives out of it," Senators winger Nick Foligno said.
The Senators jumped ahead 1-0 on their initial shot 4:52 into the opening period when Alfredsson collected a loose puck near the boards, cut inside the left circle and beat Thomas with a wrister stick side. They made it 2-0 on Michalek's power-play goal just under 3 minutes later.
With Marc Savard off for high-sticking, Bruins center Patrice Bergeron injured his right leg blocking a shot and fell to the ice, creating a 5-on-3 when he had trouble getting up, and Alfredsson passed it from the behind the net to Michalek, who scored with a wrister from the right circle.
Bergeron limped to the locker room, but returned late in the period.
Krejci's goal cut it to 2-1 just 59 seconds into the second when he tucked a backhander under the crossbar.
Boston dominated play in the opening minutes of the second, collecting another half dozen good scoring chances, before Ryder beat Elliott with a wrist shot inside the far post on the to tie it.
Elliott was fortunate to keep the Bruins scoreless in the opening period. Boston's Derek Morris hit the post and Alfredsson made his splendid play when he lunged to poke the puck away from Mark Recchi just as he was about put it into a wide-open net with Elliott caught out of position.
It was Thomas' longest inactive stretch since he also missed six games in December 2007. ... Ottawa RW Chris Neil missed his second straight with a left knee injury.