Playing alongside Ryder Cup captains Colin Montgomerie (Europe) and Corey Pavin (US) at the Jinji Lake Golf Club, Thongchai made his mark by sinking short putts for birdies at the par-four 16th and par-three 17th.
Kim later joined him on top of the leaderboard with birdies at his two closing holes - the eighth and ninth.
Thongchai was back in action after an elbow injury caused him to withdraw in the second round of last week's US Masters.
"If my health stays okay over the next few days I hope to get better and better," the Thai told reporters.
"I hit a lot of fairways and greens and made a lot of putts today." Kim followed up victory on his home tour last week by reeling off eight birdies and an eagle.
"I played very well, it was my third 64 in three weeks," said the Korean.
Woolly hats were the order of the day on a cold and windy morning that must have felt more like Scotland than Suzhou to the early starters but China's Liang Wenchong and Pablo Larrazabal of Spain set a hot pace.
Both players had seven birdies and a bogey to shoot 66s, a score matched later by Briton Jamie Donaldson.
One stroke further adrift on 67 were Irish pair Damien McGrane, the 2008 winner, and Peter Lawrie, Hong Soon-sang of South Korea and American Pavin.
World number 16 Henrik Stenson of Sweden and US PGA champion Yang Yong-eun of South Korea carded 68s.
Chinese amateur Zhang Jin, 14, the youngest player to qualify for the $2.5 million European Tour event, opened with a creditable 73.
The teenager looked very much at home early on, playing a fine tee shot to 15 inches at the par-three sixth and reaching the ninth tee at two under. But he slipped back with bogeys at the ninth, 14th and 18th.
Montgomerie had to settle for a 72 despite carding six birdies.
