Westwood collected eight birdies and two bogeys including one at the last at Royale Jakarta Club to finish 16 under par, well clear of Thailand's Thitiphun Chuayprakong and Korean Park Hyun-bin.
Having come back in the morning to finish the final two holes of his second round, a change of putter then paid dividends for the Englishman.
"It feels much better using the conventional putter because every decent putt seems to go in and that made me more comfortable," said Westwood.
"I've been in this position before and I'll try not to get ahead of myself. I'm here to win a tournament. World rankings seem to take care of themselves."
Thitiphun shot a three under 69 and Park a two under 70 to finish 11 under, while Thai Prayad Marksaeng is one shot further back on ten under following a 69.