Marcellus Sommerville added 18 points and six rebounds for the Braves (22-10), who join fellow Missouri Valley Conference member Wichita State in the round of 16. They will play the winner of top-seeded Memphis and ninth-seeded Bucknell in Oakland, Calif., on Thursday.
Playing in their first NCAA tournament in 10 years, the Braves have looked like seasoned veterans with surprising wins over fourth-seeded Kansas and now the Panthers (25-8), becoming the first No. 13 seed in the regional semifinals since Oklahoma in 1999.
They didn't wait to make the six-hour trip back home to Illinois to start celebrating.
As the horn sounded, the Bradley players leaped over the scorer's table and joined thousands of red-clad Braves faithful in the stands.
O'Bryant, a sophomore from Blaine, Minn., led the way after rendering Pitt's 7-footer a non-factor on Sunday, getting Gray in early foul trouble with his quickness and then simply outplaying him in the second half.
After dominating the smaller Kent State in the first round with 17 points and 13 rebounds, Gray had to look eye-to-eye with O'Bryant in this one, and couldn't measure up, scoring 12 points and grabbing just four rebounds.
Pittsburgh senior Carl Krauser had 17 points and six turnovers for Pitt, which was playing in its school-record fifth straight NCAA tournament, but looked like nervous kids against the newcomers from Bradley.
Krauser said before the tourney started he was looking forward to a possible rematch with former Pitt coach Ben Howland and UCLA in the regional final.
But that will be for Bradley to dream about now.
There were only 24 teams in the tournament the last time Bradley advanced to the third round in 1955. It lost to Colorado that year, ending the school's bid for three title-game appearances in five years.
The Braves raced out to a 16-4 lead behind O'Bryant's inside presence and Pitt's 1-for-10 start from the field, then really took control in the second half.
O'Bryant and Sommerville combined for all 13 of Bradley's during a 13-2 run in the first six minutes of the second half that put the Braves in control.
Sommerville capped the burst with a 3-pointer that gave Bradley a 43-35 lead with just over 14 minutes to play.
Freshman Levance Fields, who scored 18 points, stopped the run with a layup, but Pitt's misery continued. Gray missed a dunk and then Krauser missed a wide open tip-in.
O'Bryant followed on the other end with a thunderous alley-oop dunk and Tony Bennett banked in a mid-range jumper for a 53-39 lead with under 9 minutes to go.
The Panthers came right back with a 10-1 run that made the score 54-49 with 5 minutes to play. But they never got closer than four points the rest of the way, as Bradley hit big free throws down the stretch.
Pittsburgh appeared to be caught flat-footed by Bradley's hustle and determination, just as Kansas was on Friday, turning the ball over five times in 4:30 and missing its first seven shots.
The Panthers committed careless turnovers, missed free throws and lost their composure throughout the game. Krauser, playing in his ninth NCAA tournament game, came unglued several times and Gray picked up a technical foul in the second half when he slammed the ball to the court after being whistled for a five-second call.
Lawrence Wright, who had 14 points and nine rebounds for Bradley, out-leaped the taller Panthers for several offensive rebounds underneath in the first half, setting the tone for the latest Bradley upset.
That Bradley even made the tournament is remarkable in itself. The Braves started the conference season 2-4 and finished in sixth place during the regular season, but won seven of their last eight to get an at-large bid.