PHILADELPHIA – It didn’t take Jeison Rosario long Saturday night to realize Julian Williams wouldn’t be able to hurt him.

Rosario recognized immediately, too, that Williams wouldn’t be able to take his power for long. Williams didn’t appear hurt by any of Rosario’s shots until the Dominican underdog’s right-left combination wobbled Williams with about 2:10 to go in the fifth round.

Williams stumbled backward after absorbing those shots near the middle of the ring. That led to the bigger, stronger Rosario finishing the heavily favored defending champion and pulling off a huge upset in a fight FOX televised from Temple University’s Liacouras Center.

Philadelphia’s Williams was at least a 30-1 favorite according to most Internet sports books. Rosario determined long before the opening bell rang that the handicappers had this one entirely wrong.

“I realized that I had Williams when they offered me the fight[KI1] ,” Rosario told a group of reporters after recording his career-changing victory. “I knew that if I sacrificed 16 weeks in camp that I would do what I did. I didn’t realize it when I got in the ring. I actually realized it 16 weeks ago, when they offered me the fight.

“It really wasn’t about Williams. It was about myself. I knew if I got the proper time to train, like they gave me this time, I knew I would get to camp for 16 weeks like I did. It was not really about Williams. I didn’t say, ‘I’ve got Williams because of this and that.’ No, I knew I was gonna win because they gave me enough time to train, 16 weeks, and you saw the results.”

The 24-year-old Rosario (20-1-1, 14 KOs) didn’t record a knockdown after landing that aforementioned combination because referee Benjy Esteves rightly ruled that Rosario shoved Williams to the canvas with 1:48 remaining in the fifth round. Esteves understandably stopped the action after a vicious right uppercut and left hook by Rosario knocked a fast-fading Williams into the ropes.

Williams clearly was hurt, yet still standing when Esteves stepped in to end their scheduled 12-round, 154-pound title fight. A staggered Williams didn’t protest Esteves’ stoppage at 1:37 of the fifth round.

Rosario took the IBF, IBO and WBA championships from Williams (27-2-1, 16 KOs, 1 NC), who won those titles from favored Jarrett Hurd in Williams’ previous match May 11 in Fairfax, Virginia.

Unlike Hurd, who passed on an immediate rematch with Williams, the 29-year-old Williams plans to exercise his rematch clause quickly and take his second shot at Rosario in his next fight.

“Rosario was the better man [Saturday night],” Williams said. “It was a great homecoming for my fans and I’m sorry I let them down. What went wrong [Saturday night] needs to and will be fixed. We’re going to an immediate rematch and we look forward to returning the favor.”

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.