Westwood shared top spot with Kang Wook-soon of South Korea with a group of four players, including Britain's Chris Williams, a stroke behind. Darren Clarke is six strokes off the pace with 72.
Westwood, who arrived in Macau on Wednesday after his efforts in the Masters, notched up six birdies to break the record of four-under-par 67 set last year both by defending champion Satoshi Oide of Japan and Fiji's Vijay Singh.
"I wasn't aware it was a course record," said Westwood, who added that he had not really adjusted to the time change and tired at the end of the round.
Kang, who was the Asian PGA No 1 player last year, had an eagle and five birdies to match Westwood's score. "I worked hard last winter and I have been practising very hard," said the South Korean.
One stroke behind were the South Korean Choi Kyung-jun, Thailand's Prayad Marksaeng, Williams and the American Andrew Pitts. Defending champion Oide shot a one-under-par 70 to finish in 16th place.
This is the second year that the tournament has been held in the Portuguese enclave, which reverts to Chinese rule in December.
In Portugal itself, England's Van Phillips survived the worst the Portuguese weather could throw at him to claim the lead in the first round of the Estoril Open. The 27-year-old from Maidenhead battled through gusting winds, torrential rain, sunshine and even a brief hailstorm at Penha Longa to fire an opening 69 and set the early target.
Three birdies in the first four holes gave him the perfect start and he fought back well after consecutive bogeys to play the back nine in one under with a birdie and eight pars, despite the return of the strong winds which had forced yesterday's pro-am to be cancelled.
That left him one shot ahead of playing partners David Carter and Ireland's Paul McGinley, who also mastered the conditions to post rounds of 70, two under par, along with South African Retief Goosen, making his comeback after breaking his arm skiing earlier this year.
Phillips, who claimed his first European Tour win in the Algarve Open last month, joked: "It's a pity not every event is in Portugal. I'd have settled for that before the start. It was horrible for the first few holes this morning - cold with wind and rain. It was probably a two-club wind and on some holes you had to hit some really risky shots, aiming 30 yards left of the green and just hoping the wind will blow it back.
Justin Rose's troubles had earlier continued with a six-over-par 78, although the 18-year-old battled well after being five over after his first six holes.