The 21-year-old carded a six-under-par 66 at the Linkou International Golf and Country Club near Taipei to edge ahead of playing partner Kim Gi-hwan of South Korea (67) in second spot.
Asian Tour rookie Sam Brazel of Australia and India's Chiragh Kumar hit four-under-par 68s to sit in a tie for third place in the $500,000 (£316,000) event.
Thitiphun, who started on the back nine, made a brisk start with an eagle on the 10th before offsetting seven birdies with three bogeys in an eventful round.
"I eagled the 10th hole and from there I felt confident," Thitiphun told reporters. "I was lucky with the putter but I'm still not feeling very confident with my driver because I made a swing change two weeks before the start of this event."
Thitiphun, who is chasing a maiden Asian Tour victory, hoped the time spent working on his fitness during the mid-season break from June to September will help open his account.
"I worked hard during the break. I spent five to six hours practising golf and another hour and a half at the gym," he added. "I feel stronger now and I hope that this will help me win my first Asian Tour title."
Reigning Order of Merit winner Thaworn Wiratchant of Thailand, who has 15 Asian Tour titles, was tied for the fifth spot following a three-under-par 69.
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