Wade Ormsby, Prayad Marksaeng, Boonchu Ruangkit and Unho Park are knotted in third place at 5-under-par 67 at the Masters Course at Laguna National Golf and Country Club.
Mamat began on the back nine Thursday and birdied the 11th hole when he ran home a 10-footer. He knocked a 5-iron to 12 feet to set up birdie at the par-3 12th, then played a 9-iron to 10 feet at the next hole to polish off three birdies in a row.
'That good start really gave me the push,' acknowledged Mamat.
Mamat parred 14 and 15, but returned to form on 16. At the 445-yard, par-4 hole, Mamat hit an 8-iron to 25 feet and holed the birdie putt from the fringe. He collected another birdie at the par-3 16th when his 5-iron tee ball stopped 12 feet from the hole.
Mamat, a former winner on the Asian Tour, which is co-sanctioning this event with the European Tour, found trouble off the tee at the par-4 18th. His 3-wood drive found water and he could not save par.
The bogey at 18 must have shaken Mamat as the 38-year-old parred the first five holes of his second nine. At the sixth, Mamat wedged his approach to 3 feet and kicked in the short birdie putt.
Mamat hit a 4-iron to 20 feet and rolled in yet another birdie putt at the par-3 eighth. He drove into a bunker at the ninth and needed a rules official to confirm it was a waste bunker. The official did that, meaning Mamat was allowed to ground his club. He hit a 7-iron inside 2 feet and tapped in the birdie to reach minus-7.
'If you shoot 65 anytime, it's always good and it'll give me confidence,' said Mamat. 'My putting worked for me today. I'm very happy with my performance today.'
Fraser played the course from the first tee and recorded his first birdie at the par-4 fourth. He made it two in a row with a birdie at five, then added one more birdie at the par-5 seventh.
The 27-year-old birdied the par-5 11th and par-4 13th to get within two of Mamat's lead. He joined Mamat atop the leaderboard with an eagle at the 563-yard, par-5 15th.
Fraser parred out to remain tied with Mamat.
A pair of Australians, Peter Fowler and Marcus Both, were joined in seventh place by Englishman Gary Evans on Thursday. The trio finished 18 holes at 4-under-par 68.
Defending champion Nick Dougherty headlines a group tied for 10th place at 3-under-par 69. Wei Chih Lu, Miguel Angel Martin, Anders Hansen, Fredrik Widmark, Gary Murphy and Malaysian Open champion Charlie Wi joined Dougherty four shots off the pace.
Dougherty is not terribly concerned about his first-round deficit as he faced worse last year. Colin Montgomerie shot a 65 in the first round in 2005, while Dougherty only managed a 68.
'I am one shot worse than last time when Monty was on 7 under, this time it is Mardan,' said the 23-year-old Dougherty, who is paired with Mamat for the first two rounds. 'I am in good shape and it is also good to be playing with someone who is in the lead at the moment.'