BOSTON -- After winning the previous three games at home, St. Louis Blues goaltender Jake Allen turned aside 39 shots to help his team snap a three-game road losing streak with a 4-2 win against the Bruins in Boston.

"I thought the second period was the best we've played on the road and then we needed the goalie in the third and he came through big-time," Blues coach Ken Hitchcock said of Allen's fourth straight win.

The Blues fell behind twice but turned things around and won for the eighth time in their last nine visits to TD Garden.

Down 2-1, St. Louis got second-period goals from Robert Bortuzzo (his first of the season) and Paul Stastny 2:12 apart in the second to grab the lead. Allen stopped 17 shots in the third period to improve to 9-3 on the season.

"I thought in the second period we had a lot of participants," said Hitchcock. "We're still not there yet, but the second period was a marked improvement from what we've been playing on the road before.

"It was a direct contrast to the first period. I thought we had a soft start in the first period and then we dialed it up and played really well in the second."

Allen has allowed six goals on 141 shots during the four-game winning streak.

Jori Lehtera, who scored the Blues' first goal, scored into an empty net with 1:16 left to salt the game away for St. Louis -- his second and third goals of the season.

The St. Louis' win spoiled a special night for Boston's David Backes, who played 10 years with the Blues and was their captain when he signed with the Bruins as a free agent. Backes scored the game's first goal, only his second since scoring twice in the team's opener.

"I'd give it back if you could tell me we won the game. That's for sure," Backes said. "That's what matters. Wish there would have been a couple more so we could have come out on top."

Backes, who has now scored against all 30 NHL teams, gave the Bruins a 1-0 lead on a power play 7:44 into the game. Then, after Lehtera tied it 3:23 into the second, Dominic Moore scored a short-handed goal, his fifth goal of the season, to give Boston the 2-1 lead 8:59 into the period.

But the Bruins, playing without injured captain and defenseman Zdeno Chara, who left early in the second period with an undisclosed injury, were sloppy in their own end. That left goaltender Tuukka Rask alone too often as he suffered only his third loss in 14 starts.

There was no word after the game on what happened to Chara.

"Hopefully it's very temporary and he'll be back in short order," said Backes. "But if he's not we need guys to pick up slack & move forward."

They clearly struggled without Chara, with his defense partner, rookie Brandon Carlo, on the ice for both goals.

"I struggled a bit in the second," Carlo said. "Some onus on me for goals. I need to play the right way regardless of who's across from me."

"In the second period, we had five (defensemen) and we got caught in our own end for long periods of time -- and some of those guys were out there tired," said Bruins coach Claude Julien.

Rask, who stopped Jaden Schwartz on a breakaway in the first period, made 24 saves for the Bruins, who fell to just 4-4-0 at home, where they had won three straight after a 1-3 start.

Defenseman Colton Parayko had two assists for St. Louis.

Torey Krug took the shot that was rebounded by Backes to start the scoring. Krug picked up his 100th assist and David Krejci, who had the other assist, notched his 484th career point -- tying him with Don Marcotte for 15th on the Bruins' all-time list.

NOTES: Blues LW Alexander Steen didn't make the trip and missed his third straight game with an upper body injury. ... RW David Pastrnak, Boston's leading goal scorer with 10, also missed his third in a row with an upper body injury. ... Blues coach Ken Hitchcock, asked about facing former Blues captain David Backes, said: "I think it might be different for the players. For us coaches, after the first shift is over, he's another player on the team." ... The Blues are at Washington on Wednesday night, while the Bruins are at Ottawa and come back to host the Calgary Flames on Friday night.