Late in the first period of hockey's version of Armageddon, Montreal winger Yvon Lambert, the pride of Drum-mondville, Quebec, stood behind his opponents net and contemplated the puck, untouched in front of him. Boston defenseman Mike Milbury, who relishes such opportunities, promptly skated, shoulders high, into Lambert and crushed him into the boards, snapping his head back against the plexiglass.

Lambert slumped to the cold Forum ice, stunned and momentarily removed from the world of the alert. But if he'd known what would happen two-and-a-half hours later, Lambert would have felt no pain.

For after 69 minutes and 33 seconds of hard-fought, intense struggle, Yvon Lambert took a perfect cross-ice pass from teammate Mario Tremblay and without hesitation slipped the puck between the pads of Bruin goalie Gilles Gilbert. The shot gave Montreal a 5-4 come-from-behind win and the sudden-death semifinals-winning goal that the 17,453 in attendance and most of Canada had been praying for.

Having survived their closest brush with elimination in four years by edging once-and-probably-not-future Bruin coach Don Cherry's skaters four games to three, the Canadiens now move on to the NHL finals, where they will face the upstart New York Rangers beginning tomorrow night.

For a while, a long while, it looked as though the Bruins just might pull it off, gaining their first post-season victory in Montreal since 1971 and the pure satisfaction of outlasting their nemesis from up north.

But no. With time running out in regulation and Boston nursing a 4-3 lead achieved when Rick Middleton stuffed a backhand under Ken Dryden's stick-glove at 16:05 of the third, Guy Lafleur showed what makes him follow in the skate-steps of Howie Morenz, Rocket Richard and Jean Beliveau. He calmly circled in his own zone, resisting the urge to panic, then flashed down right wing and played give-and-go with Jacques Lemaire.

Then, from about 35 feet out, he blasted a low missile past Gilbert's right side to give the Canadiens life with 1:14 remaining. Montreal's situation had not been hurt when the Bruins were whistled for too many men on the ice 1:20 earlier.

Lafleur had been the impetus behind Montreal's late comeback from a 3-1 deficit as the third period began. At 6:10 he circled the Boston cage, then spotted Mark Napier streaking netward and gave him a perfect set-up. Two minutes after that, Lafleur repeated the trick as Guy Lapointe tied it from the point.

Old vets Wayne Cashman and Jean Ratelle gave Boston a two-goal edge in the second period with tallies from in close. Middleton, who ended up with four points on the night, opened the scoring 10:09 into the contest by flipping a loose puck past Dryden, but Lemaire reversed the trick by slipping a shot into the Boston net four minutes later.