Thompson stayed in Germany after receiving an offer to be a sparring partner for Vitali Klitschko in his preparation against Juan Carlos Gomez, and agreeing to face local journeyman Adnan Serin on the undercard of Klitschko vs. Gomez. Thompson defeated Serin by fifth-round TKO. Thompson then agreed to face Chazz Witherspoon on December 5, 2009, at the Boardwalk Hall in Atlantic City. Coming into the bout, 28-year old Witherspoon had 26–1 record (18 KOs), with his only defeat being a third-round DQ loss to Chris Arreola. The fight was aired live on HBO on the undercard of the fight between Paul Williams and Sergio Martínez. Thompson dominated Witherspoon from the opening bell, ultimately winning by TKO after staggering Witherspoon with the right hand in round nine and following up with a barrage of unanswered punches, prompting the referee to waive it off.