The world number three made eight consecutive pars before birdies on holes 18 and three followed by two closing birdies for 11-under-par 133 at the $750,000 Asian Tour event.
Westwood, who finished third at this month's Masters, is five shots clear of Kieran Pratt of Australia, who posted a sparkling 65 at the Royale Jakarta Golf Club.
Zaw Moe of Myanmar was on eight-under through 12 holes, three behind Westwood, before play was abandoned at 5:27 pm local time due to the threat of lightning.
Play was also suspended earlier in the day for two hours and 20 minutes for the same reason.
Moe will be among 74 players who will return at 6:30 am Saturday to complete their second rounds.
Westwood, who played in the morning, struggled with the humidity but believes the extra rest will give him an edge over the chasing pack.
"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."
"I'm glad I finished. I can relax this afternoon and prepare for the weekend," said the Englishman, according to an Asian Tour press release.
Pratt three-putted for bogey on his opening hole but made a brave comeback with 10 birdies against two more bogeys for a 138 total.
It was a polished performance from the Australian, who shot an opening 73. "I was frustrated yesterday. I felt like I was sort of playing OK but didn't putt very well," he said.
Leading second round scores (par 72):
133 - Lee Westwood (ENG) 65-68
138 - Kieran Pratt (AUS) 73-65
139 - Shiv Kapur (IND) 68-71
140 - Daisuke Kataoka (JPN) 72-68, James Byrne (SCO) 73-67
141 - Thanyakon Khrongpha (THA) 71-70, Prom Meesawat (THA) 72-69
142 - Baek Seuk-Hyun (KOR) 72-70, Antonio Lascuna (PHI) 70-72, Ajeetesh Sandhu (IND) 70-72, Gaganjeet Bhullar (IND) 72-70, Rick Kulacz (AUS) 69-73, Angelo Que (PHI) 69-73, Anirban Lahiri (IND) 74-68, Panuphol Pittayarat (THA) 74-68