Serbia's Milorad Cavic moved a step closer to a rematch with Michael Phelps in the 100m butterfly on Friday as he led the way into the semi-finals at the swimming World Championships.

Cavic won his heat in 50.56sec, while Phelps won his in 50.90, joint second-quickest overall alongside fellow American Tyler McGill and three-hundredths of a second faster than Australian Andrew Lauterstein.