Lemieux had a goal and two assists to become the first player in the National Hockey League to score 100 points this season.
But it was Coffey, recently returned to the lineup after being out with a knee injury for more than two weeks, who dominated the game.
Coffey is considered an outstanding offensive defenseman. Holding out with the Edmonton Oilers, he missed the first month of the season, then was traded to the Penguins and was injured before he reached peak condition.
In this game, he was outstanding. He took charge after Lemieux's league-leading 47th goal gave the Penguins a 4-2 lead in the second period.
With the Blackhawks trying to cut the deficit on a power play, Coffey took a pass from Lemieux and went in alone to beat goalie Bob Mason from point-blank range.
Coffey, who assisted on the Penguins' first goal, completed a hat trick with two goals in the third period. After scoring only one goal in his first 13 games, he has 4 goals and 16 assists in 14 games.
The Penguins' third victory in a row after a 10-game winless streak, put them in a tie with New Jersey for fourth place in the Patrick Division.
Buffalo 5, Boston 3--Christian Ruttu, the center from Finland, celebrated being named to the Wales Conference All-Star team by setting up four goals at Buffalo.
The Bruins, who missed a chance to take over first place in the Adams Division, apparently wore themselves out fighting. They managed only one shot in the last 20 minutes.