Klitschko inflicted the first defeat of Arreola's career
Ukraine's Vitali Klitschko retained his WBC heavyweight title with a 10th-round stoppage over the previously unbeaten Chris Arreola in Los Angeles.
Arreola, 28, failed to come out for the 11th round having been out-fought by his 38-year-old opponent who takes his record to 38 wins and two losses.
Klitschko dominated with his superior reach and despite a brief rally in the eighth round was rarely troubled.
"It's never easy. You have to be at your best," said Klitschko.
Arreola had been unbeaten in 27 fights and was hoping to become the first Mexican-American to win a major heavyweight title.
He caught his opponent in the fourth and made an energetic start to the fight.
But despite his impressive work-rate he failed to overcome Klitschko's superior reach, height and power and after getting a battering in rounds nine and 10 his night was over.
"I worked my butt off to be the champion but Vitali's strong, he hits hard and I never wanted to quit. That's never in me, I wanted to go the full 12 rounds," said Arreola.
"I couldn't get to him, he was fighting the fight he was supposed to fight. He ran when he was supposed to and I just couldn't get to him.
"Whatever I did he found a way to counteract that. He found a way to win and I found a way to lose."
Klitschko was fighting in the United States for the first time since defeating Britain's Danny Williams in 2004.
And the Ukrainian admitted at being impressed with Arreola's durability.
"Arreola had his chance, he had a great performance and I was very surprised," said Klitschko.
"He had a great chin and after my right hook, many opponents go to the floor but he still stayed up. Big respect.
"All my left jabs he was very well prepared for."