The playing partners, who started the day trailing by one, posted matching three-under-par 68s to seize a one-shot advantage over local amateur Natthaphat Harnchokchaiskul with their three-day total of 10-under-par 203s at the Thai Country Club.

Despite slipping out of the lead for the first time this week, Natthaphat held his head high after registering a second straight 70 as he stays on track to become the first amateur winner on the Asian Tour since 2009 at the US$300,000 event.

The 41-year-old Chawrasia, playing in only his fifth start on Tour this season, is chasing for his seventh victory while Martin, 35, is eyeing a breakthrough on the region’s premier Tour. The last foreigner to win the Kingdom’s National Open is Korea’s K.T. Kim in 2015.

Thailand’s Phachara Khongwatmai and American John Catlin carded identical 69s to settle three shots off the pace in fourth place with young Thai Suradit Yongcharoenchai (70), who secured his maiden Asian Tour win in Chinese Taipei last month.