The overnight leader birdied the 18th hole to snap a string of eight pars and picked up three more shots for a two-day total of 11-under 133 before play was temporarily suspended because of lightning at the Royale Jakarta Golf Club.
"It was very hot and humid early on and I suffered with that a little bit," said Briton Westwood. "It is just one of those things where it can be so hot that you can't replenish the fluids. That's Asia for you. I'm going to have to fluid up this afternoon," added the Englishman who finished third at the Masters earlier this month.
"I thought it was quite tricky out there. There wasn't much wind but the flags were placed in tough positions. If you got close, you would still have a lot of break on the putt.
"You want to be leading tournaments and I obviously got the hang of playing on this golf course. More importantly, I was patient and I didn't force things to happen," said Westwood.
Australian Kieran Pratt was five shots adrift, returning a sparkling 65 after a poor opening round of 73.
"It is only two rounds in so I need to keep going through the weekend. Obviously, Lee is a world class player and he is not going to back up but we are going to go out there and chase him," said the 23-year-old, in his second year on the Asian Tour.