They have raced together often enough to respect each other's ability and will to win.
Come next April's Commonwealth Games in Gold Coast, Chad le Clos and Joseph Schooling are expected to lock horns again in the 100m butterfly, and the South African is relishing the prospect of renewing his rivalry with Singapore's swim star.
"What he did last year was unbelievable but I love the competition, I love to race against the best," said le Clos, who was second in a three-way tie in the 100m fly (51.14sec) at the Rio Olympics behind Schooling (50.39).
"That will probably be the biggest race of the Games. We've also got James Guy (the Briton who won a joint-bronze with Schooling in July's World Championships) swimming exceptionally quick and, of course, I want to win.
"But you know, if Joseph goes under 48sec for the fly, I'm not going to beat him. So I can only control what I can control and get myself in the best shape to try and win."
The 25-year-old is in Singapore for the final leg of the eight-leg Fina/airweave Swimming World Cup taking place today and tomorrow at the OCBC Aquatic Centre.
The Fina World Cup is an international series of eight meets held in the short course (25m pool) format.
Le Clos currently holds a commanding 129-point lead over Russia's Vladimir Morozov in the overall standings after winning all his races in the 50m and 100m fly.
He was beaten only once when he finished second behind American Tom Shields in the 200m fly in the Hong Kong leg last month.
Le Clos, who will compete in the 200m fly today and 100m fly tomorrow, is almost assured of bagging the US$150,000 (S$203,400) prize money if he wins the overall men's title. That will be the icing on the cake in his "redemption" year after a disappointing 2016.
His preparations for the Rio Olympics were disrupted by news that his parents were stricken with cancer. But he showed great fortitude to bounce back and win the 200m fly gold at the Worlds in Budapest, Hungary in July.
"I think a lot of people doubted me after losing last year, they thought I was done," said le Clos, who is bidding to become the first man to win the Fina Swimming World Cup four times.
"But this year is my redemption and now that I'm back on top, I just want to stay there as long as I can and be the best Chad le Clos I can be."
Other swim stars here for the Fina World Cup include Hungary's three-time Olympic champion Katinka Hosszu and Sweden's Sarah Sjostrom, the Rio Olympics 100m fly women's champion.
Singapore will field a team of 40 this weekend, including SEA Games champions Amanda Lim, Roanne Ho and Teong Tzen Wei.
Said Lim, who has competed in the Singapore leg for 11 straight years: "It's going to be my first meet of the season so it will be good to see where I am now in my training ahead of next year's Asian Games."