Pittsburgh rookie Mario Lemieux lived up to all his advance billing by scoring two goals tonight. It was another French Canadian, less touted and lesser paid, who was the hero, however.

Washington's Gaetan Duchesne set up third-period goals by Bob Gould and Bob Carpenter that carried the Capitals to a tense 5-4 victory over the Penguins. With the triumph, Washington took over undisputed possession of first place in the Patrick Division, one point ahead of Philadelphia. The Flyers were tied in Detroit, 1-1.

The Capitals outshot their hosts by 30-10 over the last 45 minutes and so dominated the final minute that Pittsburgh goalie Denis Herron could not yield to a sixth skater until the buzzer was sounding.

"Even though we went into the third period tied, 3-3, we knew we'd win," Duchesne said. "That's our type of game. We knew with our type of team and our type of forechecking that we could control them."

Now the Capitals are faced with the task of doing it once again, since the Penguins visit Capital Centre Thursday at 7:30. Goalie Bob Mason will put his seven-game winning streak on the line in that one, after Pat Riggin posted his 16th success tonight.

"Winning the first one is the big thing," Gould said. "Now we have to go home and apply the same kind of pressure. Sometimes when you win the first game, you relax, and we can't do that."

If they weren't relaxing at the start tonight, the Capitals certainly lacked their usual fire. Outshot, 13-2, in the first 15 minutes, they were fortunate to be even, as Dave Christian's 16th goal offset Doug Shedden's 21st for Pittsburgh. In the process, Christian was extending his point-scoring streak to nine games.

Sharp passes by Craig Laughlin set up goals by Alan Haworth (No. 13) and Mike Gartner (No. 27) as Washington moved ahead, 3-1, early in the second period.

Pittsburgh caught up by putting two of its four shots in the period past Riggin. Rod Buskas hit from just inside the blueline, then Lemieux connected on a classic breakaway.

Taking Bryan Maxwell's headman pass at the Washington blueline, Lemieux skated in on Riggin. The youngster shifted the puck almost from post to post as he came in front, leaving Riggin on his knees, with his stick flat on the ice trying to cover most of the net. In that situation, it is no problem for a 6-foot-4, 200-pound center to carry the puck through a 5-9, 163-pound goalie.

"Lemieux is a great talent," said Washington Coach Bryan Murray. "He has great vision on the ice and he's sneaky fast. Give him a step and he'll beat you."

Still, Lemieux doesn't work as hard as Duchesne. Hardly anyone does. A third of the way into the final period, Duchesne fought off two Penguins, dug the puck off the rear boards and fed Gould in front. Herron knocked the puck off Gould's stick, but he retrieved it and scored.

After Gould dumped Maxwell in the left wing corner, Duchesne repeated the earlier formula and fed Carpenter in front for the eventual game winner. It was Carpenter's 32nd, matching his career high, and eased the pain of a bruised right hand that needed treatment afterward.

The Penguins were not finished, since Lemieux netted his second of the night with 5:02 remaining and Washington's Larry Murphy off for tripping. But the Capitals' relentless forecheckers made certain Pittsburgh did not score again.

Duchesne, Carpenter and Gould were united in the third period for what Murray considered the best possible matchup against Lemieux and linemates Warren Young and Wayne Babych, neither of whom put a shot on goal tonight.

"A guy like Gaetan is so valuable defensively," Murray said. "And when he gets to play with guys who can score goals, he does a heck of a job offensively, too."

The Penguins, who played tonight without five injured players, figure to be worse off Thursday. Defenseman Moe Mantha, Pittsburgh's best player over the first 30 minutes, was forced to leave with a charley-horse in his right leg.