Cotto's heavier punches quickly took their toll on Gomez (right)
Miguel Cotto battered challenger Alfonso Gomez to retain his WBA welterweight title and set up a fight with new IBF king Antonio Margarito.
Puerto Rico's Cotto made it 32 wins from 32 fights with the 26th knockout of his career, sending Gomez to the canvas for the third time in the fifth.
Margarito knocked out Kermit Cintron on the same bill in Atlantic City.
The Mexican pummelled the champion from the start, ending the fight with a left to the body at 1:57 of the sixth.
"They promised me Cotto and they'd better deliver," said Margarito, now 36-5 with 25 knockouts. "I want to be prepared for anyone, especially Margarito," Cotto added.
Promoter Bob Arum has targeted 26 July as a date for the clash.
Margarito, who handed Cintron the only previous loss of his career three years ago, had a cut over his left eye for the last three rounds but it never seemed to bother him.
He opened a cut under Cintron's left eye in the fifth. By that time, Cintron was already on his way to defeat.
The fight ended quickly in the sixth after Margarito landed a dozen solid punches, then sent the uppercut directly into Cintron's ribs.
The American who was born in Puerto Rico and represented the island in the fight, went down on all fours and never came close to getting up.
"My hands were up high and he hit me with an uppercut and I couldn't breathe," said Cintron.
"I should have tried to box more and stayed on the outside, but I wanted to prove something. I'll be back."
Antonio Margarito (right) was always in control against Cintron
Cotto was making the fourth defence of the title he won on 2 December 2006 by knocking out Carlos Quintana.
In the third and fourth rounds alone, Cotto outpunched Mexican Gomez 108-23, and two of the knockdowns came on body shots.
A straight left to the face late in the fifth provided the third knockdown.
"I tried to do everything in this fight. Work on my punching and put pressure on him," said Cotto.
Gomez was disappointed he was not allowed to continue, saying: "The doctor said I couldn't see out of my right eye."