Ryan Ohliger, who missed a 36-yard field goal in the fourth quarter, kicked a 35-yarder on BC's first possession of overtime. Then, after Jad Dean's point after try was blocked on Clemson's second possession, Ohliger split the uprights for the game-winning PAT and BC (2-0, 1-0 Atlantic Coast Conference) stormed the field to celebrate.
It was the first home victory over a ranked team for BC coach Tom O'Brien in 10 seasons at Chestnut Hill.
Clemson (1-1, 0-1) was called for offensive pass interference in the second OT, leaving it with a second-and-26 from the 41. But Will Proctor hit Chansi Stuckey with back-to-back 20 yards passes to put the ball on the 1.
James Davis punched it in on second down. But Dunbar came through the middle to deflect the point after and give the Eagles an opening.
Jeff Smith returned a kickoff 96 yards for a touchdown and also had three other long runbacks for BC; his 213 return yards was one shy of the school record. Matt Ryan, who didn't practice with the first team most of the week because of an ankle sprain, was 22-for-38 for 212 yards and a touchdown.
Proctor completed 25 of 40 passes for 343 yards and two touchdowns, hitting Stuckey 11 times for 124 yards. James Davis ran 24 times for 93 yards and two TDs for Clemson.
BC trailed 10-0, 17-7 and 24-17. Last year, the Eagles took a 10-0 lead in their first-ever ACC road game before beating the Tigers 16-13 in overtime.
BC linebacker Brian Toal left the game with a sore shoulder.
Clemson took a 24-17 lead on Davis' 1-yard run with 8:20 left in regulation thanks to two late hits that extended an 80-yard drive. Smith set BC up on its own 42 with a 29-yard return.
Ryan brought BC into Clemson territory and hit Kevin Challenger at the 14 yard-line, but Michael Hamlin took the ball away from him for what the officials called an interception. The replay review gave BC the ball back and Ryan hit Tony Gonzalez, who dove inside the 1.
On the second quarterback sneak, Ryan made it in and it was tied 24-all with 4:59 left.
Smith muffed Clemson's first kickoff, forcing BC to start from its own 8, but he followed with returns of 45, 39 and 96 yards to keep the Eagles in the game.
BC fell behind 10-0 early but had a chance to take the lead midway through the second quarter when Andre Callender broke free for 15 yards to the Clemson 2 yard-line. On the next play, he was stopped at the line of scrimmage and, when he reached out with the ball to try to break the plane of the goal line, the ball was knocked free for a fumble.
Two plays later, Proctor threw a short dump pass to C.J. Spiller, who broke several tackles on the right side before cutting across the field and sprinting down the left sideline for an 82-yard touchdown that made it 17-7.