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PITTSBURGH -- The reigning NHL MVP is out indefinitely with an upper-body injury. The league's top-scoring defenseman is out, too, apparently because of a lower-body issue.

Still, it hardly matters for the streaking Pittsburgh Penguins.

Sidney Crosby scored his 13th goal, Joe Vitale added his first in more than a year, and Tomas Vokoun stopped 31 shots as the Penguins beat the Boston Bruins 2-1 on Sunday for their ninth straight win.

"It seems like it's always different guys, so that's what you need in order to have success consistently. We've been getting that lately," Crosby said. "Our depth is a big part of our success. We need to continue to show that."

The Penguins moved into the top spot in the Eastern Conference even without star center Evgeni Malkin -- who missed his fifth consecutive game -- and played the final two periods without defenseman Kris Letang, who didn't return after the first intermission following a seemingly innocuous collision with Boston's Brad Marchand.

The Bruins took advantage of Letang's absence by spending most of the game's final 40 minutes working in Pittsburgh's end of the ice. Still, they had nothing to show for it thanks to the Penguins' suddenly responsible defense.

Taken to task by coach Dan Bylsma for sloppy play following a comeback win over Philadelphia on March 7, Pittsburgh has responded by allowing just five goals in five games.

Barely 24 hours after shutting out the New York Rangers 3-0 behind No. 1 goalie Marc-Andre Fleury, Vokoun showcased why the Penguins traded for him during the offseason to give Fleury an experienced backup.

Having guys in front of Vokoun who played smartly with the puck instead of trying to make the spectacular play certainly helped.

"They played pretty sound defensively, you've got to give them that even though their top guys (were out)," Marchand said. "That makes it a little bit tough to play against, but we've got to find a way."

Tyler Seguin scored his 10th goal for Boston, and Tuukka Rask made 16 saves but couldn't stop the Bruins from losing to Pittsburgh for the second time in less than a week.

The Penguins scored three times in the final 7 minutes Tuesday to steal a 3-2 victory. There were no dramatics necessary this time as hockey's hottest team never trailed to remain unbeaten in March.

"Our team defense has been a focus for us and how we play, and it's everybody," Bylsma said. "The responsibilities of our forwards in the defensive zone has been a key for us both offensively and defensively. In the defensive zone we're six guys defending there."

Crosby nearly netted his most spectacular goal of the season midway through the first period with a breathtaking rush in which he split a pair of defenders and then attempted to slip a shot under Rask while falling to the ice.

Rask stuck out his right pad to make the save, leaving the NHL's leading scorer to flash a wry grin.

The smile grew wider seconds later, when the Penguins won the ensuing faceoff, and Pascal Dupuis' crossing pass gave Crosby a wide-open net for the goal at 12:06.

"In a perfect world I'm pushing side-to-side, but things happen quick sometimes," Rask said. "I just lost my footing a bit and couldn't make it."

Seguin tied it 4:32 later when a shot from the point deflected off teammate Patrice Bergeron's skate and trickled right to him. Seguin had no trouble one-timing a shot past Vokoun.

Pittsburgh, the NHL's highest scoring team, moved back in front 2-1 when Vitale chipped a rebound over Rask for his first goal since Feb. 26, 2012, against Columbus -- a span of 38 games for Vitale.

Asked if he intended to flick the puck just under the crossbar, Vitale laughed.

"Oh God no, I'm just trying to put it in the net, just try to find somewhere," Vitale said. "I knew he was sliding across but I knew I had to put it somewhere upstairs but I really wasn't going for that spot."

The lead held even with the Penguins playing the final two periods Letang. With the league's top-scoring defenseman out, the Penguins geared down a bit offensively, taking fewer chances than usual.

Boston's best chance to score over the final two periods came on a wraparound attempt by Seguin that slid across the goal mouth. The Bruins would get no closer, with Crosby providing a fitting ending by getting on his stomach to block a centering pass just before time expired.

"Thought we had a chance to win," Boston coach Claude Julien said. "We spent more time in their end and we did all the things right except we couldn't get that goal. There was a couple of times where the goalie was out and we shot a puck and it looked like it was going, it hits a skate and goes wide and you get those games, you get those nights."

Game notes

Boston center David Krejci left the game with 5:14 remaining after taking a slap shot off his right knee but Julien said he didn't think it was serious. ... In addition to Malkin, the Penguins also scratched D Simon Depres and D Robert Bortuzzo. ... The Bruins scratched D Aaron Johnson and LW Lane MacDermid. ... Both teams return to the ice on Tuesday when Pittsburgh hosts Washington and Boston plays at Winnipeg.