The 28-year-old Prom ended a thrilling day at Mission Hills Golf Club's Olazabal course in tied 12th place on seven-under-par 137 but rued a poor back nine which cost him a higher finish in the US$7 million event, Asia's richest.
Countryman Thongchai Jaidee fired a 68 for tied 17th place alongside China's Wu Ashun while Thaworn Wiratchant, the current Asian Tour number one, shot a 70 for equal 31st position.
Prom turned in 32 on his outward nine but ran into trouble coming in, dropping three bogeys before shooting his fifth birdie of the day at the seventh to end the day tied with four of Europe's Ryder Cup stars Martin Kaymer, who is the title holder, Lee Westwood, Ian Poulter and Peter Hanson.
"After my first nine holes, I was nine under for the tournament and I was thinking that I'll have three par fives coming up. I was aiming for two birdies there and looking at four more birdies. So I'm disappointed getting to two over there," said Prom, who is currently seventh on the Asian Tour's Order of Merit.
A three-putt bogey on one led to him on the bogey train. He dropped another easy shot on three after a poor chip and then failed to get up-and-down from the greenside trap on six. The Thai was particular upset with the bogey on the par five third hole.
"I hit my second shot 20 yards past the hole and I thought I could still make birdie but left my third shot still short of the green and the fourth shot was six feet to the hole and I missed the par putt. I was really disappointed with that," said Prom, who will play the third round with Luke Donald and Bill Haas.
Although he trails runaway leader Louis Oosthuizen of South Africa, who shot a sparkling 63, by nine shots, Prom is only four strokes back of joint-second placed Adam Scott of Australia and South Africa's Ernie Els.
"Louis is playing amazing golf. My goal is to get a few under after every round, now I'm three shots ahead of my goal. So I'll try to keep doing what I'm doing. I'm still not looking at the leaderboard, I'll just stick to my game plan and see what I can do. Just go out there and enjoy the round. If I can shoot under par, I'll be happy," said Prom.
Three-time Order of Merit champion Thongchai was satisfied with a 68 which put him on 138 but ran into some trouble on the fifth which cost him a double bogey.
"I'm playing good. Played solid ... had eight birdies, one double and two bogeys. Four under is a good round. The greens were a bit softer and you can see the low scores," said the former paratrooper.
"I had a bad condition on the fifth hole on the left side. I complained about that hole as the area is very wet but there is no casual (water). There is no grass, just a lot of sand. You have no shot there. It's a tight lie.
"Two more rounds and I'll try to get my best. The leaders are quite far away now. I'll just keep at it, hole by hole. If I can attack, I'll do it. My putts were not too good today, sometimes it was tough to read the lines."
Thaworn will enter the weekend rounds in equal 31st place alongside names such as world number five Justin Rose. "It was better today with a two under round but I didn't hit it good. Played safe and then I was two over after six holes. On seven, I made eagle from the bunker, about a 40 yard shot which was very nice," he said.
"I'll try to stay under par tomorrow [Saturday]. I'm not looking at the leaderboard. Just keep playing my own game."