Endres who entered with the score tied at 14, led UConn (2-2) to scores on the first four drives of the second half.
He finished 7 of 11 for 139 yards and two touchdowns, including a 56-yard pass to Mike Smith that gave the Huskies a 24-14 lead. Smith caught four balls for 130 yards and that score.
Ed Young had three catches, all for touchdowns, for the Bulls (1-3). His 7-yard catch made it 24-21 in the third quarter after Endres fumbled inside the Huskies' 10 yard line.
But Endres responded by leading UConn on an eight-play, 60-yard scoring drive, capped by a 9-yard touchdown run from Robbie Frey.
Frey rushed for 112 yards on 13 carries, all in the second half.
Connecticut jumped out to an early 7-0 lead when Dwayne Grate tipped a Jerry Davis pass and linebacker Jerome Junior took it 27 yards for a touchdown just 1:26 into the game. Junior had two of four UConn interceptions.
Frazer was 4 of 4 for 63 yards on UConn's first drive, a 10-play, 80-yard march that ended with a 4-yard run by D.J. Shoemate. It was the first UConn touchdown for the junior transfer from Southern California, who started in place of an injured Jordan Todman.
Frazer, however, was just 3 for 13 after that, and the UConn offense managed just 27 yards the rest of the half, prompting changes at both quarterback and tailback.
Buffalo's Jerry Davis found Young for two second-quarter touchdowns to tie the game at 14.
Young beat double coverage down the right sideline for a 60-yard score that made it 14-7, and grabbed a 1-yard touchdown pass with 36 seconds left in the half, a play that was upheld by replay officials.
The tying score was set up when Devonte Shannon picked off a tipped pass by Frazer at the UConn 20 yard line. It was Frazer's final throw of the game. Endres came in for the last play of the half.
Davis was 18 of 42 for 227 yards with three interceptions, two which went for touchdowns. He also ran for 57 yards on 12 carries.
Endres was reinstated to the team this week after serving a monthlong suspension for an unspecified violation of school policies. The junior played in seven games last season, starting six, and threw for 1,354 yards and six touchdowns, before suffering a shoulder injury that ended his season.
Frazer came into Saturday's game having completed 52 percent of his passes this season, but for an average of just more than 150 yards a game.
Buffalo has yet to defeat a Bowl Subdivision team this season. The Bulls have also lost to Baylor and Central Florida after shutting out Rhode Island in the opener.
UConn has now won 10 of the last 11 meetings with the Bulls, including a 38-20 victory the last time the two programs met: the 2009 International Bowl.