Denis Potvin scored goals 34 seconds apart in a four-goal first period in leading the New York Islanders to a 6-5 victory over visiting Quebec last night, ending the Nordiques' seven-game winning streak.

With Quebec leading, 2-0, Potvin got the Islanders even, scoring his first goal at 7:06 and his second at 7:40. On his first score, the Islanders' captain beat Quebec goaltender Richard Sevigny on a weak wrist shot from the blueline. The tying goal was a 20-foot shot through the pads of a screened Sevigny.

The loss ended Quebec's bid to tie an NHL record for victories to start a season, held jointly by the 1934 Toronto Maple Leafs and 1975 Buffalo Sabres. The Nordiques were also the last undefeated team in the NHL this year.

The Islanders led, 4-3, after one period despite being outshot, 17-7. Quebec got goals from Michel Goulet at 3:13 on a power play and from Paul Gillis at 5:13 to take its 2-0 lead and, after Potvin's goals, regained the lead on an unassisted goal by Randy Moller at 14:21. But the Islanders made it 3-3 just 28 seconds later on a goal by Mike Bossy and broke the tie at 16:26 on a slap shot by Tomas Jonsson.