ST. LOUIS -- Tim Thomas took a relaxed attitude toward a start that was looking dicey.
"There are two ways you can go in that situation," Thomas said. "You can either start trying harder or you can relax. Today, I decided to relax and that turned out to be the right move."
Brad Marchand scored twice Thomas finished with 30 saves for Boston.
"That's just who Timmy is, that's the way he does things," Lucic said. "He puts a lot of pressure on himself to make the big save and tonight he did that."
Despite the win, the Bruins are still 8-9-1 in their past 17.
Chris Stewart and Ryan Reaves scored for the Blues on the first five shots of the game, but Thomas stopped the next 27 shots to give the Blues their first regulation loss to an Eastern Conference team in 15 games this season.
St. Louis, 26-4-4 at home, last lost at home in regulation 5-2 decision to Chicago on Dec. 3, 2011.
Marchand and Milan Lucic scored in the first period to give the Bruins a 2-0 lead. Marchand pushed the lead to 4-2 midway through the third period with his 21st goal of the season.
"This was a big win for us after being shut out in the last game," Marchand said. "With a couple of losses in a row, we wanted to make sure we followed up with a good game."
Chris Kelly, who assisted on Lucic's goal, broke a 13-game scoreless drought with his 15th goal of the season, tying a career high and putting the Bruins up 3-2 lead with 40 seconds left in the second period.
"I thought we played really well that whole second period," St. Louis coach Ken Hitchcock said. "We just couldn't get that goal even when we had all the play in their zone."
Thomas and the Blues' Brian Elliott gave up a combined five goals on 16 shots in the first period.
"I just think we needed to be better all around," Elliott said. "Myself included. We need to be mad about this a little bit and learn from it."
Elliott, who entered the game with a league-leading 1.56 goals-against average, fell to 20-7-2 and lost for the second game in a row after a five-game winning streak.
Referee Ian Walsh left the game early in the second period after suffering a cut that required medical attention. He returned 5:13 later. ... The Blues open a six-game road trip Thursday night in Nashville. Coach Ken Hitchcock is winless (0-11-6-1) in his last 18 games in Nashville. ... Elliott made his fourth successive start, tying a season high. ... The Bruins were making their first to St. Louis since Nov. 23, 2009. ... Boston has a league-best plus-33 scoring advantage in the third period.