Trent Frederic's tiebreaking goal in the third period Tuesday lifted the visiting Boston Bruins past Pittsburgh 2-1, ending the Penguins' winning streak at six games.

The teams split games on back-to-back nights.

With the game tied at 1 since late in the first period, Frederic, just off the bench, made use of a screen by teammate David Pastrnak and, from the high slot, beat Pittsburgh goaltender Casey DeSmith glove side at 7:07 of the third.

Pastrnak also scored for the Bruins, who had lost two straight and five of seven. Dan Vladar, making his regular-season debut and first career start, stopped 34 of 35 Penguins shots.

Brandon Tanev scored for Pittsburgh. DeSmith made 31 saves.

Penguins center Evgeni Malkin left in the first period with an unspecified injury. Malkin, riding an eight-game points streak entering the night, took a hit in the corner from Boston defenseman Jarred Tinordi. He stayed down a few seconds but finished the shift before leaving for the locker room. There was no penalty.

Malkin returned and took a shift on a power play later in the first, but then left and was not on the bench to start the second period.

Pastrnak gave Boston a 1-0 lead on a power play at 3:20 of the first. He moved in from the left circle, shifted from backhand to forehand and slipped it under DeSmith's pads. That gave him 13 goals in 20 games after he missed the first seven games.

Just after a Pittsburgh power play ended, Tanev tied it. Kasperi Kapanen took a shot from the left-wing boards. Evan Rodrigues deflected it, and Tanev got his stick on it for another tip, this one past Vladar at 15:02 of the first.

There was no scoring in the second, thanks at least in part to staunch penalty killing by the Penguins.

Tanev was given a five-minute boarding major penalty when he hit Tinordi, who went hard into the boards in front of the Bruins bench. Tinordi was helped off the ice and left the game. Pittsburgh killed the five-minute power play.

--Field Level Media