The seventh-seeded Panthers (24-9) outscored Louisville 12-2 to start the overtime, and their 74-64 lead with 30.9 seconds left was their biggest of the game.
DeJuan Blair added 16 points and eight rebounds for Pittsburgh, which has been to the last two tournament finals and six of the past seven. The Panthers are now 4-0 at Madison Square Garden this year, and 21-8 dating to the 2001-02 season.
Young's basket with 1:50 left in regulation gave Pittsburgh a 62-60 lead, and Clark's putback with less than a minute to go knotted the game.
After a timeout, the Panthers held for the last shot - but may have held too long. Levance Fields made a move to the basket with just over 5 seconds left and got caught in the corner, where he heaved up a contested shot at the buzzer that clanked harmlessly off the rim.
Fields scored six of his 13 points in overtime, though, and Ronald Ramon also had 13 for Pittsburgh.
That the game came down to the final minutes should come as no surprise for these two teams. Pittsburgh beat Louisville by five in the first round of the 2006 tournament, and by six in last year's semifinal, when the Cardinals were also a No. 2 seed.
Their only meeting earlier this season was a back-and-forth affair that ended after Padgett and Andre McGee each made a pair of free throws in the closing seconds to seal a 75-73 victory at Pittsburgh.
The two teams swapped the lead 10 times in the first half and were tied eight times, before a late burst gave Louisville a 33-30 at the break.
The Panthers used a 9-0 run midway through the second half to build a 51-43 lead, but Blair picked up his fourth foul a couple minutes later and Louisville closed in. Terrence Williams' basket with 4:44 to go gave the Cardinals a 56-55 lead, and the two teams matched baskets through the end of regulation.
It was another maddening trip to the Garden for Louisville coach Rick Pitino. The Cardinals are just 1-3 in conference tournaments since joining the Big East, and Pitino fell to 3-8 in his career against the Panthers.