Els, the winner of three majors, made four birdies and two bogeys at Sentosa Golf Club's 7,169-yard, par-71 Serapong course to bring his three-day total to 8-under 205.
Scott, who trailed Els by three strokes after the second round, shot a mistake-free 5-under 66 including five birdies.
England's Lee Westwood was eight strokes off the lead after an even par 71, while former U.S. Open winner Michael Campbell of New Zealand is out of contention after dropping six bogeys and a double bogey for a disappointing 76 and three-day total of 10-over 223.
Australia's Brad Kennedy (70) was in third place at five-under 208, one stroke ahead of China's Liang Wen-chong (68).
India's Shiv Kapur (72) was six strokes off the lead in fifth place, while Anthony Kang (71) of the United States and Thailand's Prom Meesawat (70) were a stroke back.
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