Vancouver, which squandered a 2-0 first-period lead, failed to gain ground on the Kings, whom they trail by six points in a battle for the final Smythe Division playoff spot.
The Kings lost Sunday to the Hartford Whalers, 6-3.
Hawerchuk scored the game-winning goal at 10:51 of the second period, beating goaltender Richard Brodeur, who had 46 saves.
Of his team's first-period deficit, Hawerchuk said: "Two goals isn't bad. It was still early in the game and we knew if we just stayed with them and plugged away we'd get our chances."
Washington 4, Boston 3--Gaetan Duchesne scored his second goal of the game with less than two minutes left to give the Capitals the victory at Landover, Md.
The Capitals moved to within one point of the second-place New York Islanders in the Patrick Division. The teams meet twice in the next five days.
Duchesne's second goal, at 18:02 of the third period, was scored after Boston's Mike Milbury had tied the score at 16:22.
The Rangers, in breaking an eight-game winless streak against the Blackhawks, scored four first-period goals to chase Chicago goaltender Murray Bannerman.
Bob Sauve, who hadn't played since Feb. 22 because of an injury, replaced Bannerman in goal for the last two periods.
Chicago lost leading scorer Denis Savard, who has 84 points this season, when he was shaken up in the first period on a check from Ranger defenseman Jeff Jackson.
A spokesman said that Savard, who had to be helped off the ice, suffered a contusion in the lower back and was taken to Lenox Hill Hospital for X-rays to determine if he broke his ribs.
Buffalo 3, Detroit 2--Scott Arniel tipped in a Mike Ramsey shot from the point midway through the third period to give the Sabres the victory at Buffalo, N.Y.
The Sabres overcame a 2-1 third-period deficit on goals by Arniel and Shawn Anderson to end a four-game losing streak and pull within three points of idle Quebec in the battle for the final playoff spot in the Adams Division.
Bob Probert and Shawn Burr scored for the Red Wings, who could have clinched a playoff berth with a victory. Lee Norwood, who had two assists in Detroit's 3-0 win over Chicago Saturday night, assisted on both goals.
Pittsburgh hasn't won at the Spectrum since Jan. 20, 1974.
Brad McCrimmon gave the Flyers a 2-1 lead when his slap shot from the left point deflected off a defender's stick past Pittsburgh goalie Gilles Meloche at 7:43 of the second period.
Tim Kerr padded the Flyers' lead when he scored his 53rd goal with 45 seconds left.