Felix Trinidad surprised Oscar De La Hoya tonight by winning a majority decision that made him king of the welterweights in a showdown that appeared to be going De La Hoya's way through nine rounds. Trinidad, the International Boxing Federation title-holder, added De La Hoya's World Boxing Council title while improving his record to 36-0 as De La Hoya suffered his first setback in 32 fights.

Jerry Roth scored the bout 115-113 for Trinidad. Bob Logist had it 115-114 for Trinidad. Glen Hamada had it even at 114. The decision brought an outburst of boos from De La Hoya's large following. But the difference in the fight, according to the judges, was Trinidad's strong finish. He won the last three rounds on two of the judges' cards.

De La Hoya appeared to be dancing and jabbing his way to victory, but weakened in the final three rounds. Trinidad's hard punches took their toll in the late going, although De La Hoya's corner was certain he merely had to survive the 12th round to win a decision.

The biggest upset of all was that Trinidad was able to win a close fight by decision in Las Vegas. Most observers believed that decision so close would go to De La Hoya. There were no knockdowns in the fight.

"I always said from the beginning that I as the number one welterweight," Trinidad said. "I was going to prove it and I did tonight. It took me time to go through my game plan but in the last four rounds he was on the run."

De La Hoya said: "My tactic was to take his confidence. I know I won. He's a great fighter. Very strong. I hurt inside emotionally. I hope we can do it again. I thought I had the fight easily. I wanted to demonstrate a boxing show, but I guess it didn't work. Some people didn't appreciate my boxing lesson. Next time I'll be a brawler. I'll be back."

The packed 12,000-seat arena at the Mandalay Bay hotel rocked with a Latin flavor and fervor. Two Latino cultures collided in support of the 26-year-old fighters to create a remarkable din, with De La Hoya drawing wild and deafening support from fellow Mexican-Americans, and Mexicans, who combined to outnumber a similarly passionate Trinidad following of flag-waving Puerto Ricans chanting their hero's nickname "Tito, Tito." Hollywood personalities abounded among those who had secured the toughest ticket to any fight in years.

De La Hoya's setback came despite an unusually dedicated training period, according to Bob Arum, De La Hoya's promoter.

"I was worried about a couple of things," Arum said. "Frankly, Oscar hadn't been concentrating. Every camp there were a million interruptions with business. Phone calls. It was terrible. This time, he got this guy Mike Hernandez, who had been his manager, out. We didn't allow hardly anybody in camp. All Oscar did was work. He showed the commitment by going up there three months early.

"The other thing was his left hand. The left hand is his power hand and he hurt it early against Oba Carr," whom De La Hoya eventually stopped in the 11th round in his last fight, in May. "We found out that the hand wasn't being wrapped properly and we fixed that. But at the same time, we told him to take it easy with the left in camp and work more with the right. It worked out perfectly. He began hitting like thunder with his right."

The fighters spent the first minute looking for an opening. De La Hoya landed the first punch of significance, a counter hook. De La Hoya danced, fired a fast combination to the head before missing a wild hook. De La Hoya landed a second combination to the head, while Trinidad had to settle for a single jab in the final seconds.

Trinidad stepped up his movement in the second round, pressing forward more as De La Hoya backpedaled. De La Hoya landed a sneaky right hand. Trinidad began bleeding from the nose, but scored a solid hook. De La Hoya blocked a hard fight and peppered Trinidad twice to the face, finishing the round with a good right hand along Trinidad's jaw.

Trinidad continued to move forward in Round 3. De La Hoya danced away, but Trinidad caught him with a right hand. De La Hoya countered with his own right hand. The action picked up in the round's last minute, with De La Hoya scoring with a combination seconds before the bell.

Trinidad finished off the fourth round with a flurry. Earlier, he landed a sharp hook. De La Hoya, continuing to fight carefully, moving in and out, could not find Trinidad. In the fifth round, Trinidad scored twice with lefts in the first minute. De La Hoya spent most of his time moving along the ropes, trying to keep out of harm's way. Trinidad dipped forward but stepped back as De La Hoya missed a hook.

But De La Hoya scored with a crisp combination to the head, his best action in several minutes. Trinidad then missed a right hand, but in the last seconds De La Hoya didn't--he landed hard to Trinidad's face and stopped Trinidad still.

The sixth round opened with a different trend. Trinidad turned cautions. De La Hoya moved in, as if he had given Trinidad plenty to think about in the previous round. The two exchanged lead right hands. Trinidad landed two glancing blows, then got through with two lefts. De La Hoya rallied with a hard combination. Trinidad continued to press. De La Hoya scored with back-to-back jabs. De La Hoya landed a right but was short with a bigger right.

"Puerto Rico has had many great fighters like Wilfredo Gomez, Wilfredo Benitez and Hector Camacho--but all of them lost when they went into a super-fight," Trinidad's father and trainer, Felix Sr., said earlier. "What happened to them is not going to happen this time."

Trinidad gave thanks primarily to his father. "My father taught me my first punch," Trinidad said. "He taught me my second punch and my third punch. He is my manager. He is my trainer. I couldn't do it without him."