France's Francois Delamontagne, who shared the opening-round lead with Plaphol, carded a 2-under 70 and is tied for second place with England's Oliver Wilson, who shot a five-under 67 on Friday. The pair is knotted at minus-9.
Plaphol, whose first-round 65 established a new course record at Shenzhen Golf Club, began on the back nine Friday. He collected his first birdie at the par- five 12th from six feet out, then added another at 18 from slightly closer.
On the first hole, Plaphol hit an eight-iron to six feet and converted the birdie putt. He dropped his only shot at the par-four sixth when his wedge approach missed the green, but the rest was spectacular, thanks to his iron game.
All three of his additional birdies came from inside six feet. Plaphol's last birdie, at the eighth, was a six-footer that gave him a three-shot lead and a share of the tournament's 36-hole record, originally set by David Gleeson in the 2002 event.
'I birdied all the par-fives today and it's helped me over the last two days,' said Plaphol, who can become the third Thai golfer to win a co-sanctioned event between The European Tour and the Asian Tour. 'The key here is to hit fairways. If I have a chance to attack the course, then I will go for it. Otherwise, I will play it safe when necessary at the weekend.'
Plaphol has two career victories, neither on the European Tour, and played well in this event last year. He tied for third behind Stephen Dodd.
'I won an Asian Tour event in 1998 and in Japan last year, but I would love to win a European Tour event,' admitted Plaphol. 'I just have to keep playing well and hope that happens.'
Delamontagne was one-over through six holes, then got it going. He birdied three in a row from the seventh to reach nine-under par for the championship, but fatigue caught up with the Frenchman.
He parred his entire back nine and in addition to high temperatures, had another reason for running out of gas on the second nine Friday.
'I think I possibly had too much sleep last night,' he said. 'I was really tired, but I had about 11 hours in total which I think was too much and made it difficult for me to shake myself awake. I think I will have to cut down a little tonight and get to the course earlier tomorrow for some practice as I really have to try and sort out my driving.'
Wilson mixed seven birdies and two bogeys for his 67.
Simon Yates posted his second four-under 68 in as many days and is alone in fourth place at eight-under-par 136. Ross Fisher of England also fashioned a round of 68 on Friday and has sole possession of fifth place at seven-under- par 137.
Jyoti Randhawa (67) and Miles Tunnicliff (70) share sixth place at minus-six. Shiv Kapur (70) and Terry Pilkadaris (71) are knotted in eighth at five-under- par 139.
Paul Casey and Asian Tour Order of Merit leader Thaworn Wiratchant are part of a large group tied for 10th place at minus-four.
Dodd, who teamed with Bradley Dredge last week to win the World Cup for Wales, shot a one-under 71 and is tied for 25th place at two-under-par 142.
The 36-hole cut fell at even-par 144 and 67 players made it to the weekend.