Kazan - Chad le Clos threw down a cheeky challenge to US swim star Michael Phelps ahead of their showdown at the 2016 Olympics after retaining his 100m butterfly world title on Saturday.
The South African clocked 50.56 seconds for a new African record in the final as Hungary's Laszlo Cseh finished second at just 0.31 back.
It was sweet revenge for Le Clos, the 200m Olympic champion, who had lost his world crown on the wall over the same distance to Cseh in Wednesday's final, when he was edged out by just 0.20.
Le Clos punched the water in delight after his 100m victory - with father Bert celebrating wildly in the stands - in a virtual carbon copy of his 2013 triumph in Barcelona when Cseh settled for silver behind the South African.
On the other side of the world, Phelps clocked a stunning 1min 52.94 seconds to win the 200m butterfly at the US championships on Friday in San Antonio, Texas.
It's the fastest time he has produced in the event since he set the world record of 1:51.51 in 2009 - and is two-hundredths of a second faster than the 1:52.96 Le Clos swam to deny Phelps gold on the wall at the London Olympics in 2012.
"Michael swam a great time, but with all due respect, that's not so hard to do when you're swimming on your own," grinned the 23-year-old Le Clos.
Now Le Clos says he hopes Phelps, who is suspended for the Kazan worlds after last year's drink-driving conviction, will be ready to battle him again in Rio.
The 30-year-old American will be looking to add to his record tally of 18 Olympic gold medals in the Rio de Janeiro pool.
"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," added the South African.
"It's going to be another great battle in Rio and I'm looking forward to another fight like it was at London 2012."
Le Clos admitted he was relieved and happy to have retained his 100m title and had been tormented by his defeat to Cseh earlier in the week.
"I'm excited. Very excited," beamed Le Clos.
"I'm just happy that I got to show everybody that it didn't make a difference if I lost the win in the 200m fly - I was going to come back strong.
"The last three days that's all I thought about, really. It was Laszlo and the silver medal.
"It was mixed emotions when I touched the wall, it had been on my mind the whole time since Wednesday and I was obviously both delighted and relieved with the win."
Le Clos, a Manchester United fan, said he had always wanted to swim in a football stadium and his win at the home of Russian Premier League side Rubin Kazan was extra special.
"It was always my dream to play professional football, I have always wanted to swim in a football stadium and it was a dream come true for me to do it here," he said.
"It was really cool - so thanks Kazan.
"I have played football all my life and my dad went to see Manchester United in 2005. Since then I have been a fan."
Le Clos also paid tribute to Cseh, who had ended a 10-year wait for a second world title in Wednesday's 200m butterfly final.
"Laszlo is a great friend of mine and a great competitor, I have had the privilege of racing him over the years and if there is someone to look up to it's him," said Le Clos.
"He's the perfect ambassador for being a professional athlete."