Mayweather appeared at WWE No Way Out 2008 in Las Vegas, Nevada. He was involved in a storyline altercation with Big Show when Mayweather jumped a security barricade and attacked Big Show to help Rey Mysterio (whom Show had threatened to chokeslam). Mayweather originally assumed a babyface role in the story lines, which met with some resistance from fans. The attack resulted in Big Show receiving a broken nose. The following night on Raw, Big Show challenged Mayweather to a one-on-one No Disqualification match at WWE WrestleMania 24, which Mayweather accepted. At WrestleMania, Mayweather defeated Big Show in a knockout with brass knuckles, to maintain his unbeaten record. Mayweather was reportedly paid $20 million for the fight. 1,058,000 PPV buys were reported for WrestleMania 24, grossing $23.8 million in revenue.
Mayweather was guest host for WWE Raw in Las Vegas on August 24, 2009. He interfered with a tag-team match, which resulted in a loss for the Big Show (again a heel) and his partner Chris Jericho as Mayweather gave Montel Vontavious Porter brass knuckles to knock Jericho out, giving Porter and his new tag-team partner Mark Henry the win and a shot at the Unified WWE Tag Team Titles at WWE Breaking Point 2009 against Jeri-Show. He then celebrated with Henry and Porter, turning face. Later that night, he was involved in a backstage segment with Vince McMahon, D-Generation X and Carlito helping McMahon prepare for his six-man tag-team match against Legacy and DX. During the segment, McMahon knocked out Carlito.