Lost the WBA heavyweight championship to Tim Witherspoon by a 15-round majority decision on January 17, 1986. Tubbs weighed 229 pounds when he won the title, and he was criticized for going into his first title defense against Witherspoon at 244.
Fought Mike Tyson for the WBA/WBC/IBF heavyweight championship on March 21, 1988, and lost by a second-round TKO. The promoter offered Tubbs an additional $50,000 if he weighed less than 235 pounds for the fight. He weighed 238¼.