BOSTON - Tim Thomas drifted to the front of the crease to cut down the angle, leaving him out of position when the shot went wide to his right, off the boards and right to Lightning forward Steve Downie.

The Boston goalie reached back, swung his stick at the puck and caught it with the bottom edge of his blade, knocking it away to protect a one-goal lead and give the Bruins a 3-1 victory over Tampa Bay that left them one win away from their first Stanley Cup finals since 1990.

"It was just reaction and, you know, desperation," Thomas said after stopping 33 shots Monday night- none bigger than Downie's with about 11 minutes left. "I'll admit I got a little bit lucky there."

Thomas bounced back from a Game 4 collapse, and Brad Marchand scored the game-winner to help give Boston a 3-2 lead in the best-of-seven Eastern Conference finals.

The Bruins could clinch the series Wednesday night in Tampa Bay.

"Our goal right now is to not play a Game 7," Bruins coach Claude Julien said. "It's going to take our best game."

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The Lightning would need to win Game 6 to force a decisive game in Boston on Friday. Tampa Bay faces elimination for the fourth time these playoffs, having fallen behind the Penguins 3-1 in the first round.

"Our backs were against the wall before against Pittsburgh," forward Ryan Malone said. "We're not going to be able to win two games in one game. So you try to go out there, worry about the first five minutes of the game and you take it from there."

Simon Gagne, who scored the game-winner for Tampa Bay in Game 4, scored just 69 seconds in. Nathan Horton tied it for Boston in the second period, 17 seconds after returning from the penalty box. Marchand scored with 4:04 left in the period to give Boston a 2-1 lead.

Tampa Bay finally managed to pull the goalie with 42 seconds left, but Rich Peverley scored an empty-netter with 12.1 seconds left to clinch it. The Lightning left the extra skater on the bench for the ensuing faceoff, but they couldn't come through with anything more than some shoving after the final whistle.

Boston managed just 19 shots on Mike Smith as he made his first career playoff start in place of Dwayne Roloson.

Smith said he didn't expect to play.

"I figured that Rollie would be back in," he said. "He's done well the whole playoffs. I was ready to go if called upon. Rollie's been great, he's been here and done this and any advice that he gives me is stuff that I just suck in like a sponge. Obviously he's a great mentor."

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Thomas bounced back after allowing four straight goals in Game 4 and may have saved the season when he stopped Downie on the edge of the crease. The crowd cheered each time it was shown from a different angle on the scoreboard, and Thomas could even be seen smiling through his mask when the camera cut to him.

"That's just a confident swagger. He definitely has that," Bruins forward Chris Kelly said. "It's a game. You've got to have fun with it. It's a great opportunity for all of us. If you're not going to enjoy it, you might regret it."

Two nights after Tampa Bay rallied with five goals in a row to overcome a 3-0 deficit and win Game 4, Boston shrugged off Gagne's goal and staged a comeback of its own.

After Gagne converted a 2-on-1 with Steve Stamkos to beat defenseman Johnny Boychuk and put the puck past Thomas, Horton tied it on a one-timer from Milan Lucic 4:24 into the second period - just Boston's seventh shot.

Marchand also took a penalty in the second and then came back to score. After Zdeno Chara kept the puck in the zone, Patrice Bergeron went to the faceoff circle to retrieve it, then passed it over to Marchand for an easy chip-in past Smith.

Smith started 20 games in the regular season and came on in relief of Roloson twice in the series, shutting Boston out for the final 18:49 of Game 2 and then coming back in Game 4 with 2:02 left in the first period after Boston took a 3-0 lead. The Lightning scored five consecutive goals, and Smith shut out the Bruins for the final 42:02 to earn a 5-3 victory.

Mike Ehrmann / Getty Images The Week in Sports Pictures The nation grieved for those hurt, killed and affected by the Boston Marathon bombings. After one of the suspects was caught on Friday — following a day-long lockdown and manhunt — sports returned to Boston over the weekend.

Smith's shutout streak lasted another 24:24 before Horton's goal tied it 1-1 in the second - a total of 85:15.

Notes: For the third time in the first five games of the series, a goal was scored in the first 80 seconds. ... New England Patriots coach Bill Belichick was in the crowd, and he was voted fan of the game. Celtics point guard Rajon Rondo was also in attendance. ... Ken Hodge, a star of Boston's 1970 and '72 Stanley Cup championships, also got a big cheer when he was shown on the scoreboard. ... The Bruins almost scored on a dump-in in the final 3 minutes when the puck took a bad bounce and rolled right across the crease, inches from the goal line, as Smith was behind the net waiting to play it. ... Boston went two entire power plays without getting off a shot. ... The Bruins are 17-4 all-time when leading a series 3-2. ... The Lightning fell to 8-2 in the playoffs when scoring first. ... The Bruins' record low for shots in a playoff game is 12, against Toronto in 1951 and against Edmonton in the 1988 Stanley Cup finals.