Andre Ward returned after 19 months out with a convincing win over Britain's Paul Smith in a non-title catchweight bout in California on Saturday.
The American unbeaten super-middleweight champion dominated from the start in his home city of Oakland.
Smith, 32, caught his 31-year-old opponent with a right in the seventh but was cut later in the round.
With Smith's face covered in blood and a suspected broken nose, his trainer threw in the towel in the ninth round.
What did Ward think of his return?
An Olympic gold medallist at Athens 2004, Ward had not fought since beating Edwin Rodriguez in 2013 because of a contractual dispute with former promoter Dan Goosen, who died in September 2014.
He became the first high-profile fighter to sign with rapper Jay Z's Roc Nation Sports in January.
Ward, who beat Britain's Carl Froch in December 2011, immediately had Smith on the back foot and, apart from getting caught in the seventh, was rarely troubled.
"It took some time to get the rust out," said Ward, who has won all of his 28 professional fights.
"I started strong with the jab. I really wanted to come out with a big bang.
"I have a great coach and he told me take your time and the knockout will come. I could see his legs getting a little wobbly."
|What is catchweight?|
|Boxers agree the weight themselves rather than fighting at a designated world-title weight.|
|Ward v Smith was fought at 172lb rather than the super-middleweight category of 160-168lb.|
'A war we didn't want to continue'
Smith weighed in 4.4lbs over the 172lb catchweight limit and reportedly had to give up a share of his purse for the fight to go ahead.
The Liverpool fighter lost every round on each of the three judges' scorecards and suffered another cut in the ninth before Joe Gallagher threw in the towel.
"Smith was taking unnecessary punishment," said Gallagher. "Andre kept cutting open that cut over his eye. Blood was pooling over his eye. It was a war we didn't want to continue."
The defeat was Smith's sixth in 35 bouts and he said: "The towel couldn't have come soon enough."
Shawn Porter survives a scare
In another high-profile non-title bout, Shawn Porter was knocked down by Adrien Broner in their welterweight fight in Las Vegas.
However, Porter gained a unanimous 12-round points decision to win and take his record to 25 wins, one draw and one loss in 27 fights, while Broner fell to a second defeat in 32 bouts.