Jyoti Randhawa fired a 64 to join Barry Lane, Gregory Hanrahan, Eddie Lee and Damien McGrane in a tie for second at 8-under-par 136.
After an electrical storm led to the suspension of the opening round on Thursday, play resumed Friday with Lee taking the first-round lead. The second round followed at Laguna National Golf & Country Club and Mamat quickly made his move up the leaderboard before darkness halted play for the second straight day.
Mamat played the back side first and tallied three birdies and a bogey over his first nine holes to make the turn at 7 under.
At the par-5 second, Mamat played his third shot to 12 feet and drained the birdie putt.
He stumbled with a bogey at the fourth but came right back with a birdie at the par-4 sixth after his approach stopped within seven feet of the cup.
Mamat closed his round in style to take the lead in the clubhouse as he dropped his second shot inside eight feet at the par-4 ninth, his last. Mamat then ran home the birdie putt to finish on top at minus 9.
'My concentration has been very good the last two rounds,' said Mamat. 'I expected weather delays and long waits but it doesn't bother me. I want to concentrate hard and take it one step at a time over the weekend.'
Lane made an impressive charge on Friday to move into contention. The veteran collected five birdies on a blistering front nine en route to a round of 65 to finish one shot off the lead.
'Twenty-three years on tour is a long time but I absolutely love it,' said the 43-year-old from England. 'I don't enjoy the travelling so much nowadays but I love the competitiveness of the tour and getting the chance to play with these fearless young lads.'
James Kingston and Kyi Hla Han finished two shots off the pace at 7-under-par 137. Peter Lawrie and Roger Chapman followed at 6-under-par 138.
Thongchai Jaidee, Michael Campbell, Henrik Bjornstad, Yuan-Chi Chen, Simon Khan, Thammanoon Srirot and Nick O'Hern finished knotted at 5-under-par 139.
Colin Montgomerie was one shot further back in a group at 4-under-par 140.
'I've only made one bogey all week so everything's fine,' said Montgomerie. 'It's hard work and you've got to keep away from the water but now I'm five behind, I can win from here.'
Defending champion Lian-Wei Zhang carded his second straight round of 72 to come in at even-par 144.