Sergio Martinez holds on to defeat Julio Cesar Chavez Jr.

With a massive lead built by years of attention to developing his jab, speed and quickness, Sergio Martinez decided he still wanted to fight Julio Cesar Chavez Jr. in the 12th round.

The rookie move nearly cost Martinez a victory he’s longed for, as Chavez knocked Martinez down in the 12th and forced him to find a final skill — fortitude — to survive and claim a unanimous-decision victory in the World Boxing Council middleweight championship bout.

Judges Adalaide Byrd and Stanley Christodoulou scored the bout 118-109 and Dave Moretti had it 117-110 for Martinez (50-2-2) as Chavez (46-1-1) suffered his first loss in surrendering his belt.

PHOTOS: Sergio Martinez vs. Julio Cesar Chavez

“I hurt him; I thought I was going to knock him out,” Chavez said after an effort that raised memories of his legendary father’s final-seconds knockout of Meldrick Taylor in 1990.

“I tried to knock him out, but he kept holding on.”

The left-handed Martinez, 37, dominated the fight until its dramatic ending by unleashing a precise, skilled performance that relied on heavy use of a crisp jab, along with timely defense and sharp lefts.

Chavez was a mess after 11 rounds.

Both eyes were swollen. Two judges had awarded Martinez every round. And the champion was repeatedly beaten to the punch, with blood streaming from his nose.

As the 10th round ended, however, Martinez gave a clue he was going to remain engaged until the end, when he closed the round by urging Chavez to fight and raising his arms to a sold-out Thomas & Mack Center crowd of 19,186 fans.

Chavez had irked Martinez by taking over as middleweight champion in 2011 after the WBC effectively stripped Martinez of the belt. Martinez despised how Chavez relied on his father’s legendary name to gain lucrative pay-per-view fights against suspect foes, andhe vowed to punish the 26-year-old.

Martinez took Chavez’s best blows earlier in the fight, and even got the best of an exchange in the 11th, emboldening his decision to stand in front of Chavez again in the 12th.

Chavez threw a left-right-left combination to knock Martinez down early in the 12th. Martinez was barely able to rise by the eight-count, and was left open to more punishment.

It appeared he was knocked down a second time, but referee Tony Weeks ruled the fall a slip. Still, Martinez was in deep trouble, and Chavez threw multiple big rights and a left to the head trying to finish the job.

Martinez held on, survived, backed away, and the final bell rang.

“I was 20 seconds away from knocking him out,” Chavez said. “I started way too late, in the eighth round.”

Martinez told Chavez in the ring afterward, “You hit me hard. You’re a great fighter.”

“He was tougher than I expected,” Martinez said. “He showed me he had a great heart. It’s great for boxing to have a champion who’ll fight anybody.”

PHOTOS: Sergio Martinez vs. Julio Cesar Chavez

Both fighters expressed interest in meeting again.

“If Julio wants a rematch and the public wants a rematch, we’ll do a rematch,” Martinez said.

lance.pugmire@latimes.com

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