The second modern-era golf tournament at the Olympics got underway at the Kasumigaseki Country Club with low scores dominating the day.
Sepp Straka, out in the very first group, set the pace with an opening-round 63 to take a one-shot lead over Jazz Janewattananond. Thomas Pieters, fourth in 2016, is a further stroke behind after a 65.
Straka, Janewattananond, Pieters top three after low-scoring day at Kasumigaseki Country Club
The 29-year old Austrian birdied four of his last six holes, including birdies on 13, 14, 15 and 17 to tie the Olympic record held by Matt Kuchar five years ago.
"If you just put it in the fairway on this course you can really take advantage and I got hot with my irons, especially my short irons and wedges. I was really knocking down the flagstick and really tried to stay aggressive with those.
"I felt comfortable with my game going into this week. I hadn't played great over on the PGA Tour the last few weeks, but my putting was really the reason and I just switched it up my routine on my putting and it's worked out."
A former Asian Tour Order of Merit winner with ten victories in his home country of Thailand, Janewattananond carded a bogey-free 64 to position himself just behind the 161st-ranked Straka.
Pieters experienced the disappointment of just missing out on a medal in Rio, but he posted a 65, the second straight round with that number going back to the final round in 2016 after four birdies and an eagle.
"Didn't play my way out of the tournament after the first day, so that's good", the Belgian said. "I was not in good ways yesterday, so I kind of didn't expect this today. My caddie told me 'hit it there' and I did it. I kept it simple."
Straka and Pieters were paired together in the first group and the Belgian said seeing Straka's outstanding play factored into his own fine score.
"That definitely helps. It's nice to see balls going at the flag and getting close to the pin."
The Austrian agreed, saying "we had a really good group, had some good mojo going in the group and first off was great. We didn't have to wait on anybody, and we played quickly. We didn't feel rushed because we had some pretty good space between us and the group behind us, so that was really key."
The chasing pack
Among those in contention are Carlos Ortiz, who tied Pieters for third with a 65, Jhonattan Vegas, firing an opening-round 66 and Paul Casey with a 67.
The bigger names lie further behind as Xander Schauffele, Viktor Hovland and Patrick Reed all shot 68 and Hideki Matsuyama, Collin Morikawa and Rory McIlroy carded 69's.
Four-under after eight holes, Matsuyama bogeyed the ninth and 11th to slide back to two-under in a tie for 20th, six shots behind Straka.
"This experience could be the first and last that I get to play the Olympics in my country", the Masters champion said. "So hopefully [Friday] i'll put together a better round."