Right wing Mike Bossy scored two dramatic third-period goals and Denis Potvin became the second defenseman in NHL history to score 100 points in a season as the New York Islanders beat the New York Rangers, 5-2, tonight.

The Islanders, who edged Montreal for the regular-season point title, learned of the Canadiens' 1-0 loss to Detroit moments before taking the ice for the third period. It took Bossy just 16 seconds to snap a 2-2 tie, as the second-year scoring star rushed behind the Rangers' net and swept back in front to nudge a five-foot shot past goalie John Davidson. Bossy added insurance at 9:23 of the session, breaking in alone and planting a 20-footer for his 69th goal of the campaign.

Bryan Trottier, the NHL scoring champion this season, scored his 47th goal of the season with 5:33 remaining to make it 5-2. Trottier, who also set up Bossy's second goal of the game, finished the year with 134 points.

Potvin picked up his 100th point of the season by feeding Wayne Merrick to tie the game 1-1 at 16:59 of the first period. He added his 70th assist and 101st point on Bossy's game-winner in joining Bobby Orr in the 100-point club for defensemen.

In other games, Ted Bulley tipped in his 27th goal of the season on a slap shot by Tim Higgins with 52 seconds remaining to give the host Chicago Black Hawks a 3-2 victory over St. Louis; Reggie Leach's power play goal at 11:52 of the second period put Philadephia ahead to stay in the Flyer's 4-2 victory over visiting Atlanta, thereby clinching the fourth-best record in the NHL; Colorado got a goal by Barry Beck with 16 seconds left to tie host Buffalo, 5-5, despite three goals by the Sabres' Jacques Richard, and the homestanding Boston Bruins rallied to beat Toronto, 6-3, behind stellar goaltending by Gilles Gilbert.