Thai golfer Kosuke Hamamoto took a surprise early lead with a six-under-par 65 in the opening round of the Singapore Open Thursday as Olympic champion Justin Rose had a disappointing start.
Hamamoto was a shot ahead of American Matt Kuchar, the bronze medallist at the Rio Olympics, Richard T. Lee of Canada, Gunn Charoenkul of Thailand and Japan's Rikuya Hoshino.
Rose was three shots behind the leader, as was Rio silver winner Henrik Stenson of Sweden.
With all three men's golf medallists from the 2016 Games appearing at the SMBC Singapore Open, it is being viewed as a warm-up for the Tokyo Olympics which start in July.
But it was 20-year-old Hamamoto -- whose mother is Thai and father Japanese -- who impressed with a strong debut performance at the tournament.
"Today I just had a lot of fun and did not really put a lot of pressure on myself," he said after the first round interrupted for over an hour due to stormy weather.
Rose, the highest-ranked player in the field at world number nine, had a shaky start with a bogey on the 10th -- his first hole of the day -- but immediately got back the shot with a birdie at the next.
The English player's game improved with three birdies on his back nine, but he was nevertheless disappointed.
"My game was not exactly great," said the 39-year-old. "I did not hit many good shots today but I think I managed my game very well."
Kuchar made the best start of the Olympic medallists.
He made an early run at the leader thanks partly to a superb eagle on the par-five seventh at Sentosa Golf Club, but a double bogey on the 13th stopped him in his tracks.
He fought back with birdies on the 15th and 18th holes to join the second-placed group.
Jazz Janewattananond of Thailand, who won the Singapore Open in 2019, got his title defence off to a good start, firing a four-under-par 67 to finish two shots behind Hamamoto.
Ten Olympians are competing at the $1 million tournament, which runs until Sunday and is jointly sanctioned by the Asian Tour and Japan Golf Tour Organization.