South African Chad le Clos backed up his Olympic 200m butterfly title with a first world championship gold medal in Barcelona on Wednesday thanks to a storming last 50m that saw him pull away from Poland's Pawel Korzeniowski.

The 28-year-old Korzeniowski looked set to reclaim the title he won seven years ago in Montreal as he turned for home in front, but le Clos reclaimed the lead with a rapid underwater burst and hung on to win in a time of 1 min, 54.32 sec.

And le Clos admitted afterwards that it was after watching Michael Phelps' remarkable eight gold medal haul at the Beijing Olympics that he realized just how important his underwater stretches could be.