The world number three won the US$750,000 Asian Tour event last year and is right on course for a repeat after his seven-under par round put him two shots clear of the field.
The early running was made by the highly-rated Arnond Vongvanij of Thailand, who set the morning clubhouse target of 67.
But it took afternoon starter Westwood just 11 holes to take the outright lead.
The Englishman, who admitted poor putting cost him the chance of Masters glory at Augusta two weeks ago, rediscovered his touch on the greens and rolled in confident birdie putts on each of the first three greens.
After turning in 31, he tied Vongvanij with a birdie at 10 and moved into the lead on his own with a two at the par three 11th.
Another birdie followed at 11 and although he dropped back to six-under with a bogey three holes later he rounded off a fine day's work with a closing birdie at the par five last.
"I had a break last week and hardly hit any balls," said Westwood. "I played a lot of golf earlier this year and needed a rest. It was good to go home and recharge my batteries because the Masters always takes a lot out of you. It is physically and mentally very demanding."
It was a wind-swept day at the Royale Jakarta Golf Club and Westwood was caught off guard on the 14th hole where he dropped his second bogey of the day.
"This is quite a tricky test because the greens are very undulating. You've got to have your "A-Game" with you. It (wind direction) changed on 14 and it caught me by surprise and ended up with a bogey where I three putted," said the Englishman, who rose to world number one with his victory in this tournament last year.
Three behind Westwood in tied third sits a six-man group featuring Indian duo Jyoti Randhawa and Shiv Kapur along with Boonchu Ruangkit of Thailand, Zaw Moe of Myanmar, Lee Sung of Korea and American Sam Cyr.