LOS ANGELES (AP) — Unheralded Josesito Lopez stopped welterweight star Victor Ortiz after nine rounds Saturday night, apparently breaking Ortiz's jaw to earn a stunning upset victory.

Ortiz and his corner stopped the fight before the 10th round could begin when the injury left Ortiz unable to close his mouth.

Lopez (30-4, 18 KOs) leaped onto the ropes to celebrate one of the biggest upsets in recent boxing history, grinning and shrugging his shoulders at the cheering crowd at Staples Center.

"I knew I had to fight the fight of my life to win," said Lopez, a Riverside native who has never fought for a world title. "I knew the longer it went, the better chance I'd have. He hits hard, but I was never going to quit. I knew it was a close fight on the scorecards, and I knew I could press him more and more if I continued. He's like a tree. I had to chop him down."

Lopez accepted the fight last month as a late replacement for Andre Berto, whose failed doping test scuttled the eagerly anticipated rematch of Ortiz's unanimous decision over Berto in a tumultuous bout in April 2011.

Ortiz (29-4-2) was narrowly leading on all three judges' scorecards when he quit, but the former welterweight champion didn't dominate as expected in his first bout since getting stopped by Floyd Mayweather Jr. last September.

Although Ortiz repeatedly tagged Lopez with shots throughout the bout, producing swelling around both of Lopez's eyes, Lopez repeatedly replied with big shots of his own — and he even taunted Ortiz with come-at-me gestures, thrilling the crowd.

"I'm a man, and I'm not intimidated by anything," Lopez said. "I have a big heart. He tried to intimidate me, but it didn't work. Victor has no heart."

Argentina's Lucas Matthysse also stopped Mexico's Humberto Soto after five rounds with a barrage of punches at the bell in a thrilling 140-pound fight on the undercard.

Ortiz was so confident of a victory over Lopez that he already agreed to his next fight: a showdown in Las Vegas in September with Mexican star Saul "Canelo" Alvarez, who watched this bout from ringside.

The Ortiz-Alvarez fight is now off, and Lopez will be among the top contenders for that title shot. Golden Boy promoter Richard Schaefer, who said he was glad Ortiz quit to avoid devastating injury, expects to announce Alvarez's new opponent next week.

The upset is an enormous setback for Ortiz, who hadn't been in the ring since Mayweather flattened him when Ortiz dropped his guard and attempted to hug the unbeaten pound-for-pound champion after a head-butt. Ortiz thinks he hurt his jaw in the fifth round, but wasn't certain.

Ortiz showcased his superior skill and power from the opening round, repeatedly putting Lopez on the retreat. Yet Lopez constantly found ways to respond, either through counterpunching or his own strong shots to Ortiz, who has never been a defensive technician.

Lopez used his longer reach to pick at Ortiz, who occasionally showed frustration in a clinch. Ortiz also hit Lopez with a rabbit punch in the back of the head, earning a caution from the referee and the jeers of fans.