EAST RUTHERFORD, N.J., DEC. 15 -- No matter what happens to the Buffalo Bills from here, one moment is sure to figure as pivotal in their future. When their starting quarterback and franchise, Jim Kelly, was forced to leave today's game against the New York Giants in the second quarter with a sprained left knee, the Bills had a decision to make.

They could fold and use the loss of the NFL's top-ranked quarterback as an excuse, or they could go on to see just how big were their hearts. Buffalo picked the latter, and with its 17-13 win over the Giants, firmly established itself as one of the top two teams in the NFL.

Played before a crowd of 66,893 on a cold, wet afternoon, the game was easily the biggest win of the year for Buffalo, and also one of the most damaging for both teams. Besides Kelly, New York quarterback Phil Simms was knocked out of the game in the third quarter when he sprained the arch on his right foot. He is questionable for next Sunday's game against Phoenix.

Kelly is out for at least the final three regular season games because of cartilage damage after linebacker Carl Banks pushed offensive tackle Will Wolford into Kelly's leg. Team doctor Richard Weiss said he doesn't expect Kelly to undergo surgery. Weiss said he won't make a final diagnosis until Sunday.

While leaving Giants Stadium, Kelly, who finished seven of 11 for 115 yards and one touchdown in 24 1/2 minutes, said, "I'll be all right."

With Kelly out, the Buffalo defense stepped up and won the game, holding New York to its second lowest point total of the year. Former University of Maryland quarterback Frank Reich replaced Kelly, hit eight of 15 passes for 97 yards and led the Bills to a field goal. Last year Reich was 3-0 in games in which he replaced Kelly after he separated his shoulder.

"The main thing is that the team has a lot of confidence in me," said Reich. "My thought was to go in and move the ball and get a couple of first downs because our defense was playing so well."

Simms injured his foot in the second quarter after being chased by left end Leon Seals. Simms eventually left with 9:59 left in the third quarter. He has a protective cast on the foot, and Giants officials wouldn't discuss the seriousness of the injury.

When asked if he would be able to play next Sunday, Simms said, "I don't know. I really can't say anything."

But team physician Russell Warren said: "Right now we're calling it a sprained right foot. It looks significant. It's a sprain of the midfoot."

Later Coach Bill Parcells said that X-rays of Simm's foot were negative.

Jeff Hostetler replaced Simms and was ineffective despite completing nine of 16 passes for 97 yards.

For the Bills -- who scored on their first two possessions -- this was an extemely important game for two reasons. One, they wanted to prove that their record, now 12-2, is no fluke. And two, they wanted to show that the AFC can be just as physical as its NFC counterparts.

"It's a special win for us," said linebacker Cornelius Bennett. "As far as playing the Giants, we'll finally get some recognition as a tough team. People thought that since we were from the AFC we must be a bunch of weaklings. We just laugh at that stuff.

"As long as we win, we'll keep making all those second-guessers look stupid."

The Giants' first score was set up by a 41-yard run off tackle by running back Rodney Hampton, his longest of the season. Their touchdown was supplied by Ottis Anderson, a bullish one-yard run up the middle.

Buffalo, with the highest scoring offense in the NFL at 28.7 points a game, immediately countered. A screen pass to Thurman Thomas turned into a 49-yard gain. Kelly later hit Andre Reed on a six-yard pass for a score and the game was tied after the Bills had the ball for only 1:28.

"Our ability to come immediately back after {the Giants'} touchdown was the most important part of the game," said Coach Marv Levy.

The Bills' defense held New York to 21 yards on its next possession. Thomas then scored on a two-yard run. The Giants managed field goals of 22 and 23 yards from Matt Bahr while Scott Norwood kicked one from 29 for Buffalo.

Then it was left up to the defense.

Which is the way Bills all-pro defensive end Bruce Smith likes it. He caused quite a stir this week by saying that Giants linebacker Lawrence Taylor should step aside and be replaced by him as "The Man" on defense. Smith was able to back his words, getting 10 tackles despite the Giants running away from him. He didn't add to his league-leading 19 sacks, but made Simms and Hostetler uneasy all afternoon.

"I just want a little credit that's all," Smith said. "I think this year I've been playing outstanding. I want to ask a little question: If they're double- and triple-teaming me, what does that say? I'm not being cocky."

The Bills play Miami at home next week, a game that likely will decide who wins the AFC East and gets home-field advantage for the playoffs. Smith called the game "The biggest game of our lives."