The Bruins started slow against a Tampa Bay team that was energized from the start.
Mike Smith made the surprise start in net instead of Dwayne Roloson for the Lightning, who have had to turn to Smith in relief in the past two games.
The Lightning got off to a quick start as Simon Gagne opened the scoring just over a minute in, finishing a quick 2-on-1 play from Steven Stamkos. It was Gagne's fifth goal and his 12th point this post-season, matching his total of last year's playoff run with the Philadelphia Flyers.
After one period, the shots were 14-4 in favor of Tampa Bay, and the Bruins weren't able to put anything up on the scoresheet.
In the 2nd, Tim Thomas and the Bruins took over.
Nathan Horton got Boston on the board after taking a pass in the slot from Milan Lucic and blasting a shot past Smith. It was Horton's seventh goal of the playoffs and his 14th point, and both Lucic and David Krejci assisted, which is much-needed support from Boston's top line.
The Lightning couldn't respond immediately on some good chances, and eventually Boston made good on their own opportunities again.
On a harmless looking play, Bruins' centre Patrice Bergeron slid the puck in front to Brad Marchand, who quickly put the puck in the net to give Boston a 2-1 lead. Zdeno Chara also picked up an assist on the play, his first point of the series against Tampa Bay.
Entering the third, the Lightning had 23 shots on Thomas, with just the one early goal finding a way though him.
The third period told much of the same story as Thomas was stellar, stopping another 11 shots through the final frame. The period was highlighted at the midway point by a Thomas save that had Lightning forward Steve Downie doubting his own eyes. On an Eric Brewer point shot, the puck deflected off the end-boards and right out in front to Downie, who had a half-open net as Thomas was down. Thomas dove across the net and Downie's shot hit his stick not once, but twice, and deflected out of the net.
The save had the nearly 18,000 fans at TD Garden on their feet, as the Lightning tried desperately to beat Thomas in the last ten minutes of play.
Finally, with the net empty, the Bolts gave the puck away to Boston's Chris Kelly, and Rich Peverley put the game away for his second of the playoffs.
The series is now in Boston's favor for the second time, after taking a 2-1 lead at the end of Game 3. The series will continue Wednesday night in Tampa Bay as the Bolts hope to stretch the series longer. Boston needs just one win to advance to their first Cup final in 20 years, and the chance to win a sixth Stanley Cup for their franchise, and the first since Bobby Orr won it in 1972.
Game 6 is Wednesday at 8 P.M at the St. Pete Times Forum. The Lightning are 4-3 at home this post-season.