RUELAS KNOCKS BALBOA DOWN AND OUT IN FIVE.

Byline: Michael Rosenthal Daily News Staff Writer

Suffering from a persistent case of flu, Rafael Ruelas a few weeks ago considered pulling out of Tuesday's matchup with Rocky Balboa at Fantasy Springs Casino here. And only hours before fight time, he was popping throat lozenges.

The last thing he needed was 10 long, hard rounds in the unusually cold night air. He made sure it didn't happen.

Ruelas put Balboa down and out with a perfectly placed left hook to the kidney 2:39 into the fifth round of a junior welterweight bout before 925 spectators. It was Ruelas' fourth straight victory since he lost to Oscar De La Hoya and George Scott last year.

``I'm happy,'' Ruelas said. ``I wanted to take my time, not get too tired. I didn't overextend myself, I was patient. And it turned out well.''

Ruelas (47-3, with 37 knockouts) didn't know much about the 34-year-old Balboa (63-22-1, 57 KOs) before the fight.

In fact, he didn't know until the ring announcer said moments before fight time that Balboa had the 57 knockouts, unmistakable evidence of a dangerous punch.

In response, Ruelas fought carefully - keeping his hands near his face at all times - as he waited for the one or two big punches it would take to get back into his warm hotel room.

At the same time, Ruelas stalked Balboa from the outset, which made it difficult for his more experienced but faded opponent to get punches off. And Ruelas landed progressively more punches as the fight went on, though neither fighter was hurt until the fifth.

In the final round, Ruelas, who had been body-hunting throughout, landed a left to Balboa's side that hurt him. About 20 seconds later, he did it again, which caused Balboa to curl up on the canvas, a typical response to a most painful punch. He couldn't go on.

``I hurt him with that first body shot,'' Ruelas said. ``When that happens, I try not to let the effect wear off.''

Afterward, Ruelas and his trainer, Joe Goossen, were talking of bigger and better things.

Ruelas, formerly the International Boxing Federation lightweight (135 pounds) champion, wants to fight for the 140-pound championship sometime this year.

In the meantime, he'd like to step up in terms of his opposition. Namely, he mentioned Julio Cesar Chavez as an opponent who could lead him to that title shot.

Chavez's promoter, Bob Arum, at one time mentioned Ruelas as a possible opponent for his fighter but has since suggested that Ruelas isn't a viable opponent. Plus, Chavez's personal problems seem to preclude any bout anytime soon.

With or without a Chavez fight, Ruelas' ultimate goal is to get back into the ring with De La Hoya, who took his title by a second-round knockout in June of last year.

Goossen believes his fighter would make a better account of himself the second time.

``Rafael was overanxious the first time,'' Goossen said, referring to the fact Ruelas came out very aggressively. ``I think (De La Hoya) can be beaten if you get into a rhythm and avoid getting caught with that big punch.

``I think (De La Hoya) loses steam on his punches after a few rounds.''