SINGAPORE - It was 1.17pm in Rio de Janeiro, slightly a quarter of an hour past midnight in Singapore on Aug 10 but it was better late than never for swimmer Joseph Schooling to deliver a National Day gift to the nation.

Swimming in Heat 6 of the 100m freestyle event, the 21-year-old powered to second place amongst eight swimmers with a new national record time of 48.27s, lowering his previous mark of 48.58s set in last year's SEA Games.

In the process, he qualified for the semi-finals as the sixth fastest swimmer. Australia's Kyle Chalmers was the fastest man (47.9), followed by the United States' Caeleb Dressel (47.91) and Britain's Duncan Scott (48.01).

The semi-final will be held later on Tuesday evening in Rio (Wednesday morning at 9.03am Singapore time).

"(National day) is a great day to start racing. It's a happy day," Schooling said after the heats.

"I was a little nervous (in the morning). But it feels different. It doesn't feel like an Olympics."

Schooling's other event in Rio is the 100m butterfly, where he is expected to reach the final and challenge Michael Phelps, Laszlo Cseh and Chad le Clos for a podium place.