Cape Town - Chad le Clos is a step closer to claiming his fourth Swimming World Cup title after a solid performance on the opening day in Tokyo.
Le Clos claimed gold in the men's 50m butterfly touching the wall in 22.49 on Tuesday.
In the men's 100m freestyle, the South African was edged by Vladimir Morozov with the Russian stopping the clock in 45.65 and Le Clos taking silver in a time of 46.09.
The 25-year-old is currently on 360 points and has a 123-point advantage over second-placed Morozov on arriving in Tokyo, and had stretched that before the end of the night.
The Rio Olympic silver medallist picked up three gold medals in Beijing last weekend.
"I was nervous a bit for the 50m fly because it was the 27th consecutive win in that event at the World Cup, and no-one's done that before," Le Clos told the fina.org website.
"It's 30 races unbeaten with the world champs. It's going to be close for the cluster with Vladimir, but hopefully - and I don't really want to say it - something would have to go really wrong for me to lose the overall title. Still, I want to win the cluster too."
Le Clos has won the Swimming World Cup three times - in 2011, 2013 and 2014 - and could become the first man to win four World Cup Series titles.
The men's and women's series winners take home $150 000 each with an additional boost for the each overall cluster winner who collect $50 000.
The second and final day of the FINA World Cup in Tokyo gets underway on Wednesday at 10:20 SA time.