Lee Westwood trailed Indonesian Masters leader Siddikur of Bangladesh by two strokes after the first round on Thursday.
Westwood birdied his last two holes to post a 4-under 68 in ideal conditions at Royale Jakarta Golf Club.
He has a chance to regain the world No. 1 ranking if he wins this week and fellow Englishman Luke Donald fails to at the Heritage on the U.S. PGA Tour. But Westwood said he was merely hoping to celebrate his 38th birthday on Sunday with a 34th victory worldwide.
Westwood says he ''played solidly but I was a bit frustrated out there. It has been the story for me so far, hitting it great from tee to green and giving myself a lot of chances but not taking it.''
Siddikur, the first Bangladeshi to win on the Asian Tour, shot 66, including two chip-ins for birdies.
A group of six players, including Thai star Thongchai Jaidee, were a stroke behind, then Westwood and six others were two behind Siddikur.