Welliver frequently gestured Williams to keep punching him and the Kiwi obliged, sometimes doing so with a smile.
He displayed his renowned durability, but offered little offensively as his wide looping punches posed few problems for Williams.
Welliver's antics prompted referee Les Fear to tell him to "stop mucking around" in the fourth round.
In Gallen's fight, the Sharks NRL forward threw some terrific uppercuts and body shots and supplemented his power punches with the occasional jab.
He rated it as probably the best performance of his boxing career, as he largely followed trainer Graham Shaw's instructions to box rather than brawl.
"I have a lot of respect for Gal, he handled himself pretty well tonight and he looked like he punches hard," said Williams.
Both Williams and Gallen suggested their proposed fight was still a possibility.
Gallen acknowledged he was still at a level below Williams.
"Sonny is probably a level above me at the moment, but I want to learn," Gallen said.
"In 12 months time I have to learn a bit to really compete with Sonny."
Sydney Roosters NRL prospect Willis Meehan (3-0, 2 K0s) maintained his pristine professional record with a second-round stoppage of American Freddy Miller (3-10-1, 2 KOs).
-AAP