Martinez won 118-110 on two ringside scorecards and 117-110 on the third. The Associated Press had him winning 118-110.
"I was 20 seconds away from knocking him out. I started way too late," Chavez said. "I didn't really get started until the eighth round."
Martinez said before the fight he didn't consider Chavez a true champion, and then he made sure Chavez didn't look like one until he ran into trouble in the final round. And what trouble it was, with Martinez coming off the canvas twice and in deep trouble when the round finally ended before a thunderous crowd of 19,186.
"He fought a great fight, and he was a lot tougher than I expected," Martinez said. "He showed great heart."
The wild ending nearly ruined what was a great night for the Argentine fighter who used his speed and boxing skills to dominate until the final round. Chavez was bleeding from the nose, his face was marked up and he looked finished until suddenly landing a huge left hook to drop Martinez for the first time.
Martinez got up only to take several more head punches and go down once again. Chavez kept after him when he got back up, trying desperately to land the finisher before the bell sounded and the decision was lost.
"If Julio wants a rematch, we'll do a rematch," Martinez said.
The comeback was reminiscent to one by his father in 1990 against Meldrick Taylor, when he came back from seemingly certain defeat in the last round to stop Taylor with 2 seconds left in the fight.
"You hit very hard," a victorious Martinez told Chavez.
Martinez fought his fight in the early rounds, using his jab and speed to keep Chavez off balance. Fighting out of a southpaw stance, he stayed on his toes, moving around on the outside and seldom allowing Chavez in where he could cause damage.
Chavez earned his biggest payday, $3 million guaranteed, while Martinez got $1.4 million plus a percentage of the pay-per-view sales.