Andre Ward lost a point for a low blow in the eighth and later drew a warning for an accidental head butt.
Not even that was enough to slow the former Olympic gold medalist's march toward a possible tight fight in his new division.
Ward unanimously outpointed Sullivan Barrera in his light heavyweight debut Saturday night, setting the stage for a potential title fight against unified champion Sergey Kovalev.
"It feels great," Ward said. "I feel like I shook off a lot of ring rust. I had high expectations for this fight but I think I got it done. I need to tighten things up. I have a lot to prove in this decision."
Ending a nine-month layoff while fighting for just the fourth time in four years, Ward (29-0) knocked down Barrera in the second round with a sharp left. The 34-year-old Cuban bounced up quickly before Ward landed another pair of stinging lefts to the head.
About the only thing to go wrong for the Oakland fighter came late in the eighth when referee Raul Caiz deducted a point from Ward for the low blow that sent Barrera (17-1) down to one knee.
All three judges had Ward winning easily. The scores were 117-109, 119-109 and 117-108.
The win paves the way for Ward to fight Kovalev, the Russian slugger who has defended his title three times since beating Bernard Hopkins in a unification match in 2014. While talks between both camps have been ongoing, things are expected to heat up now.
"Sergey Kovalev is a great champion," Ward said. "I fight the best, I always fight the best and he's just another name."
Fighting in front of his hometown crowd, Ward was the quicker fighter most of the night and used his jab to score often, mixing it with a powerful left hook that landed to the head frequently. He also ducked away from most of Barrera's punches and at one point in the sixth smiled after Barrera swung and missed twice.
Ward continued to score with his big left hand throughout the bout and drew loud cheers from an intimate but raucous crowd of 8,532 at Oracle Arena.
"We showed great boxing ability coming off this layoff," said Virgil Hunter, Ward's longtime trainer and mentor. "He showed good boxing ability, great defense and rhythm. Now it's about getting rounds in."
Barrera, the IBF's No. 1 contender going into the night, landed his own jab with some success but couldn't put much together and lost for the first time in his career.
NBA MVP Stephen Curry of the Golden State Warriors watched the fight from ringside not far from Oakland Raiders owner Mark Davis. Former NFL running back Marshawn Lynn and former world boxing champions Roy Jones Jr. and Shane Mosley also were on hand.
Kovalev, who called Ward a "gentleman, a nice man," before the fight, was in the crowd as well.
The 32-year-old Russian predicted an easy Ward win before the fight and said a matchup against the former Olympic gold medalist would be the biggest challenge of his career.
"November is a great time," Kovalev said. "Let's do it, me and him, a done deal."
Kovalev and Ward could each have another warm-up before their eventual bout which is expected to be on pay-per-view.
Had Barrera won, the picture would have been a lot more uncertain.
Although the stakes were billed as being for the expected title shot with Kovalev, Ward had a stipulation added to the contract guaranteeing him a rematch with Barrera first.
It didn't happen, setting the stage for what many are already billing as a potential fight of the year even though no deal has been finalized.
"It's going to be the opposite from Mayweather-Pacquiao in every way," said Main Events promoter Kathy Duva, whose stable includes Kovalev.
In the semi-main event, Joseph Diaz Jr. posted a 10-round unanimous decision over Jayson Velez.