Michael Phelps won his first race back following six-month suspension . The U.S. swimmer was stripped of the gold medal in the 4x100 freestyle relay on Sunday after testing positive for a banned stimulant. Olympic champion won 100m butterfly at the Arena Pro Swim Series .
Michael Phelps won his first race back following six-month suspension . Phelps was suspended by USA Swimming for failing a drink-driving test . Olympic champion won 100m butterfly at the Arena Pro Swim Series .