The Buffalo Bills may have gotten their biggest test of adversity in Saturday's 17-13 victory over the NFC East Division champion New York Giants. But it was a test the Bills would much rather do without. Buffalo overcame quarterback Jim Kelly's second-quarter knee injury and hung tough after establishing a 14-10 halftime lead to push its record to 12-2, and 3-0 against NFC opponents. Kelly led the Bills to two touchdowns and a 14-7 advantage before a freak injury with 5 1/2 minutes left in the second quarter sidelined him for the remainder of the game. But a determined Buffalo defense took over, holding the Giants to just three points in the second half, while back-up quarterback Frank Reich and the Bills offense squeezed out enough offense to hang on to a costly victory.