Two goals down in the sixth game of their Stanley Cup semifinal, the New York Islanders were feeling a tightness in the throat. They three off the "choke" label, however, be charging from behind to defeat the Buffalo Sabres, 5-2, and advance for the first time into the final series.

Four times semifinal failures in the past, the Islanders won the first three games of this series with Buffalo. When they lost the next two and fell behind, 2-0, tonight, there was wonder whether they might deserve the nasty names they were called following last year's flop against the hated Rangers.

Goals by John Tonelli and Mike Bossy matched the earlier scores of Buffalo's Gil Perreault, then Bob Lorimer netted his first goal of the playoffs to send the Islanders ahead. Duane Sutter and Bob Bourne, on an empty net, eased the churning tummies of the New York fans with third-period insurance goals.

"That was a tough series last year and we don't believe we're chokers," Bourne said. "I hope tonight we proved it."

"Those guys gave every ounce of blood, coming back like that," said Coach Al Arbour. "It showed the character of our team. Even though we were two down, we knew there was a lot of time left. We wanted to get one goal at a time and we did."

Perreault was flying around the Islanders and he gave everything he had, hitting a post and forcing goalie Bill Smith to make three tough saves in addition to his goals.He had too little help, however, with injuries keeping Craig Ramsay and Rick Dudley in the stands and with Richard Martin, as usual, proving a playoff fizzle.

Just 75 seconds after Perreault's second goal, Sutter broke down the right wing, crossed the goal line, turned and avoided Mike Ramsey's check to feed Tonelli in front.

"That first goal was really a big one," Arbour said. "If they'd gotten the next one, we'd have been in trouble, but we put a lot of pressure on them and things started going our way."

In the first minute of the second period, Bossy rebounded a drive by Bourne to convert a powerplay opportunity and tie the score. It was the only success in six extra-man chances for New York. Buffalor was zero for seven, turning around once more after failing on its first 11 tires in the series and hitting on four of the next five.

The winning goal resulted for a delayed penalty on Buffalo's Bill Hajt, who pulled down Bourne in front of the net. The puck slid into the corner and Butch Goring retrieved it. He fed Lorimer, who cut down the slot and fired from the hashmarks, then gave a rendition of an Apache war dance.

"I guess I went a little crazy after I scored it," Lorimer said. "I don't score many. I got one in the playoffs last year, but they're pretty rare.

"The delayed penalty was what gave me the chance. I saw the opening in the slot and with the delay I wasn't afraid to go in. Butch gave me the puck and that was it. It was unbelievable."

The Islanders, once ahead, did not ease up. Their continued pressure paid off when Sutter netted a rebound with 8:10 left in the game for a 4-2 lead. Buffalo Goalie Bob Sauve first blocked a shot by Sutter, then stopped Goring's rebound before Sutter connected.

"We lost the fourth game here after we were ahead 3-1 because we sat back and they took it away from us," Lorimer said. "There was no way we were doing that again."

Although this was not an especially violent series, there was one wild incident early in the third period. It occurred during a Buffalo power play and the aggrieved party was Buffalo winger Lindy Ruff, the man assigned to the rigorous slot duty, trying to screen Smith.

As the television replay later showed, Ruff was speared by Smith, cross-checked by Lorimer and, finally, butt ended by Smith as play shifted to the other end. The butt end of Smith's stick struck Ruff in the left eye and, after he fell, he rose and turned to charge at Smith. He merely pulled him down, however, with Andy Van Hellemond being dumped as well, the referee having turned back to break up the combatants. Ruff received a double minor, Smith two minutes for roughing.

"The ref said he was up ice and didn't see it," Ruff said. "I'll tell you, it was the most cheap shot I ever saw. There's a difference between knocking in front and putting a stick in the eye. I didn't do a thing. I didn't even touch him.

"The contact lens was pushed off my eyeball and I couldn't see, and I was afraid to hurt the eye, that's why I didn't really do anything. But I told him I'll be in the league a long time and I'll get him. When you live by the stick, you die by the stick."

Smith, a notorious stick swinger who has been assessed 93 penalty minutes the last two seasons, said, "I hate being interfered with. Ruff tonight speared me in the pads a couple of times when shots were coming from the blue line. You have to do something to defend yourself."

The Sabres received nine minor penalties, high for them, and one accompanied Lorimer's goal. Ric Seiling knocked the puck into the stands after Lorimer scored and was charged with delay of game.

"I went to hit the puck against the boards and it went over the glass and he called it," said Seiling, holding an ice pack to his bruised shoulder.

There was much evidence of physical discomfort in the Sabres' dressing room. If the Islanders were hurting it did not show.