Flint and Webber both had five birdies in bogey-free rounds, and the Korean-born Park had six birdies and a bogey to top the leaderboard ahead of players such as Phil Mickelson, Vijay Singh and Ernie Els.
Angelo Que of the Philippines had a 67 and was one shot off the lead at the remodeled 6,710-yard Serapong Course at Sentosa Golf Club.
Mickelson's double-bogey on the par-4 third ultimately cost him a share of the lead, and he finished at 3 under along with South Korea's K.J. Choi and Japan's Tetsuji Hiratsuka.
'I scored well and got the ball into the hole well,' Mickelson said. 'But my driving has been terrible and the worst that it's been since I started working with (coach) Butch (Harmon).
'It's 10:15 his time at night and I'm going to give him a call, wake him up. I'm lucky to escape with a three-under-par round. I'll talk to Butch to see if I can get it ironed out for tomorrow.'
Singh -- who had an eagle on the par-4 10th -- and two-time defending champion Adam Scott were among 13 players at 70.
'I seem to hit it to about 15 to 20 feet quite a lot,' Scott said. 'A few came up short, especially when you're putting down the green. But I hit some good putts, I just haven't quite got the pace down yet, that's something I have to work on.'
U.S. Open champion Angel Cabrera also recorded a double-bogey on the troublesome third hole and ended even-par, along with Darren Clarke and Lee Westwood.
Els, the European Tour money leader who elected to play this tournament instead of the Volvo Masters and thus jeopardize his chances of claiming the Harry Vardon trophy, shot a 72. The South African had a double-bogey on the par-5 seventh to go with two bogeys and three birdies.
Mickelson, who is attending the tournament after his family home in California narrowly escaped the wildfires, was surprised by the difficulty of the course and the ability of the players.
'I didn't expect the course to be that difficult,' Mickelson said. 'This is a Tour-caliber golf course. The fairways are in perfect condition, and it's tight. The rough is thick and the greens are fair and fast. It's a good test of golf.
'I haven't been made aware of how good the golf is in Asia. These players are strong.'
Six players did not complete their round and would play the final holes on Friday morning.
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