The 47-year-old, seeking a strong week to boost his chances of retaining his playing privileges on Tour next season, followed up his opening round seven-under-par 65 with a 68 to sit level with South Korean Wang Jeung-hun (65) at 11-under 133.
Last year’s Asian Tour Order of Merit winner Kiradech Aphibarnrat was two shots back in third after the Thai hit a 69, with England’s Steve Lewton (66) and Malaysian Danny Chia (71) in a share for fourth at seven-under.
Mamat, a three times winner on the Asian Tour, began his second round with 10 straight pars after starting on the 10th at the Jack Nicklaus designed Manila Southwoods Golf and Country Club.
He made a bogey at the par four second before picking up his first shot of the day at the fourth and then finishing in style with four straight birdies.
“The birdie on sixth actually got my momentum going. I hit a four iron to about two feet and I regained my confidence from there,” he said.
Japan’s Daisuke Kataoka, who shared the overnight lead with the Singaporean, fell down the field to tied for sixth at six-under after a one-over second round of 73.
Leading scores after the second round (par-72):
133 - Mardan Mamat (SIN) 65-68; Wang Jeung-hun (KOR) 68-65
135 - Kiradech Aphibarnrat (THA) 66-69
137 - Danny Chia (MAS) 66-71; Steve Lewton (ENG) 71-66
138 - Hung Chien-yao (TPE) 67-71; Nicholas Fung (MAS) 69-69; Daisuke Kataoka (JPN) 65-73; Paul Peterson (USA) 68-70; Javi Colomo (ESP) 69-69.