Around the world's top male golfer, fans sought shelter under umbrellas, officials hid behind trees and journalists clung to facial wipes.

It would have been easy for Jordan Spieth to find fault with the stifling heat at the Sentosa Golf Club yesterday.

After all, the American sensation did not sit atop the leader board after the first round of the SMBC Singapore Open, as many had predicted.

Instead, he was refreshingly honest and self-deprecating in picking apart a four-under 67 scorecard on his debut at the Serapong course.

"The humidity is fine - yeah it's hot, but it's not overbearing," the Texan told reporters, wiping away perspiration after finishing his round at the height of the midday sun.

"I didn't get many looks (for birdie), didn't get the ball inside 15 feet. I had plenty of opportunities to."

Taking advantage of free entry on opening day, a crowd of over 600 trailed Spieth for nearly five hours.

Some arrived as early as 7am, 50 minutes before his tee-off.

They were treated to glimpses of the solid all-round game that has seen the American capture the No. 1 ranking for 12 consecutive weeks and cross the US$23 million (S$32.8 million) mark in career earnings.

The 22-year-old was pleased with his "stress-free" driver, which helped to connect with 10 out of 14 fairways. But he needed 31 putts on the large undulating greens - some way off the form that led to wins at the US Open and Masters last year.

His typically red-hot irons were also a bit cold. The youngster swung his club skywards in frustration after a skewed approach shot landed 15 feet away from the pin on the par-five 18th.

Rather than attack the hole to make up for his miscue, he conservatively two-putted for birdie.

"For the positions I was in off the tee, it was a little frustrating," the seven-time PGA Tour winner reflected later.

"From there I couldn't quite get it on the right tier (of the green) or right distance, my distance control was just off trying to judge the wind, humidity and the heat."

Still, Spieth scrambled well and avoided any bogeys despite missing four greens in regulation.

Agent and manager Jay Danzi carried his bag, with regular caddie Michael Greller taking a rare week off because of injury.

" I thought he stepped in extremely well," Spieth said of Danzi, who is covering for the second time after a tournament in Japan in 2014.

"It's a tough place to caddie when you are not used to carrying the bag, what with the weather, but he took it like a champ."

Spieth sits one shot adrift of co-leaders Keith Horne and Berry Henson after the first day at the US$1 million event, co-sanctioned by the Asian and Japanese Tours.

He does not expect things to get any easier on Serapong, pointing to "the greens being 50 yards deep and 40 yards wide" and comparing it to a "pretty challenging PGA Tour event".

"My expectations were high coming in, considering how highly people have spoken of this golf course," he noted with a wry smile.

"I was curious about where pins would be, and they did a great job of putting them where grain changes on the green, which makes it tricky.

"It makes it look like it's not that hard, when it very clearly is."