Chan eagled his closing par-five ninth at the DLF Golf and Country Club to sign for a 65 while Singapore's Lam Chih Bing and Thailand's Thaworn Wiratchant took a share of third place alongside five other players on 67.
Thailand's Chapchai Nirat carded a 68 to be among the mix of nine players in 10th place that included Malaysia's Ben Leong, Australia's Rick Kulacz and Terry Pilkadaris, Taiwan's Lin Wen-hong and Thailand's Kwanchai Tannin.
Siem who is seeking his second professional win, marked his card with three birdies on the 12th, 17th and 18th in his opening back-nine to reach the turn in 33.
The German continued to enjoy another blemish free run in his homeward nine by carding another three birdies followed by a closing eagle.
"I can't remember the last time that I shot 64. It must be at least three years ago so I'm pretty happy with that. It's definitely my best round for a few years," said a delighted Siem.
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