Phelps, beware! Le Clos is here!

'It's going to be another great battle in Rio and I'm looking forward to another fight'

South African Chad le Clos threw down the gauntlet to rival Michael Phelps with a cheeky grin after powering to the 100 metres butterfly gold at the world championships on Saturday.

Defending champion Le Clos dipped under 51 seconds for the first time in his career, clocking 50.56 seconds to atone for the disappointment of missing out on the 200m gold in the week.

Although he held off great friend Laszlo Cseh of Hungary by 0.31 seconds, it was a message of intent to multiple Olympic champion Phelps -- currently competing at the US Nationals in Texas -- which lit up his news conference.

"I'm very excited for Rio next year and I hope he's in good shape, because I'm in good shape and when Chad le Clos comes at you in the last 50m, you'd better be ready," the South African said.

"It's going to be another great battle in Rio and I'm looking forward to another fight like it was in London 2012."

Phelps currently holds the 100m butterfly world record of 49.82, though it was set in 2009 in a now-banned fast suit.

In Kazan, both 29-year-old Cseh and Le Clos, 23, closed the gap significantly on Phelps.

While Le Clos set an African record, Cseh's time of 50.91 seconds in heats was the first time a swimmer had dipped below 51 seconds since Phelps winning time of 51.21 seconds at the London 2012 Olympics.

Phelps, who beat Le Clos to Olympic gold, will race the men's 100m butterfly in San Antonio.

He will do so after setting the fastest time of the year in the 200m butterfly.

"Phelps did a great time of 1min 52.94sec today, but with all due respect, that's not so hard to do when you're swimming on your own," added Le Clos.

The South African was referring to the fact that Phelps's time would have won the world title in Kazan.

South Africa moved up to ninth in the medal table with four medals.