"It doesn't matter, as long as I got the win," said Jennings, who won by scores of 115-112 and 114-113. Perez won a scorecard by 114-113.
The win makes Jennings (19-0, 10 knockouts) the No. 1 contender for the World Boxing Council heavyweight title. A win in that bout - which should take place early next year - would make Jennings Philadelphia's first heavyweight champ since Tim Witherspoon in 1986 and the second since Joe Frazier.
Jennings, knowing the scores were close, opened the final round with a fury. He used his right hand - which proved to be his favorite punch - to back down Perez (20-1-1, 12 KOs) early in the round. But Perez was then penalized, allowing Jennings to fight at ease. He threw 58 fewer punches than Perez but connected on 33 more.
Jennings rocked Perez with a right hand midway through Round 8. With 40 seconds left, the referee had to separate the two fighters after Perez clutched Jennings in the middle of the ring. Visibly agitated, Jennings stepped back and connected with a strong right.
"He wouldn't trade, I wanted him to stand in there and fight," Jennings said. "I was expecting the inside pressure of Mike Perez, and that wasn't the Mike Perez that showed up."
Jennings walloped Perez with a combination in the final seconds of the fourth round. The punches bounced Perez off the ropes for the second time in the round. After a slow start, Jennings began to appear comfortable. He attacked Perez again in the fifth round, connecting on a combination highlighted by a right uppercut that wobbled Perez in the middle of the ring.