PHILADELPHIA – Jeison Rosario will have to beat Julian Williams again before he could move toward the biggest fight for the newly crowned champion within the 154-pound division.

Sampson Lewkowicz, Rosario’s promoter, thinks that showdown with WBC super welterweight champion Jermell Charlo could happen by the end of this year, though. Houston’s Charlo had hoped to face Williams in a 154-pound championship unification bout, but Rosario stopped the heavily favored Williams in the fifth round Saturday night at Liacouras Center on the campus of Temple University.

“I believe it would be a great fight between him and Charlo,” Lewkowicz told BoxingScene.com following Rosario’s huge upset. “It’s a 50-50 fight. It’d be a great fight. And I believe that within two fights, it would be pay-per-view. We need two fights. We need to prove that he can beat his mandatory and somebody else, and then the fight with Charlo would be pay-per-view.”

Philadelphia’s Williams (27-2-1, 16 KOs, 1 NC) indicated in the immediate aftermath of his stunning defeat that he’ll exercise his rematch clause and wants it to happen immediately. If Rosario (20-1-1, 14 KOs) were to defeat Williams again, he might have to make a mandatory defense of his IBF junior middleweight title before he’d be permitted to challenge Charlo.

Russia’s Bakhram Murtazaliev (17-0, 13 KOs) is the IBF’s No. 1 challenger for Rosario’s title. That mandatory defense already is due, but an immediate rematch with Williams would supersede that mandated matchup.

“First of all, we need to wait for Williams to make a decision,” Lewkowicz said. “I will wait as long as I can to give him the rematch. But [Rosario] has a mandatory due with the IBF. I will honor the IBF mandatory if Williams decides not to take the rematch immediately.”

Charlo, meanwhile, referenced Williams’ stunning loss in a Tweet late Saturday night.

“ON HOLD AGAIN,” Charlo stated, referring to a unification fight. “LIONS ONLY WANT ALL THE BELTS. NO WAY EITHER ONE OF THESE 154 WILL BE ABLE TO TAKE THIS LION POWER.”

Charlo referred to the two other boxers that hold 154-pound titles – Rosario and Patrick Teixeira.

Rosario now owns the IBF, IBO and WBA belts. Brazil’s Teixeira (31-1, 22 KOs) is the WBO’s junior middleweight champion.

The 29-year-old Charlo (33-1, 17 KOs) won back the WBC 154-pound crown by knocking out Detroit’s Tony Harrison (28-3, 21 KOs) in the 11th round of their rematch December 21 at Toyota Arena in Ontario, California. Harrison had upset Charlo by unanimous decision in their 12-rounder almost exactly one year earlier at Barclays Center in Brooklyn. 

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