The events defending champion sank an 18-foot birdie putt on the first hole and then picked up five more birdies through the 10th at the Aloha Golf Club.
I didnt make too many mistakes and my course management was good, Westwood said. Ive got one eye on the Masters and nothing beats winning for confidence.
Danny Willett and Jan-Are Larsen were tied for second at 66.
Willett, a top-ranked amateur who received an invitation to play, had two eagles on his first seven holes. He opened on the back nine and eagled the 10th, and then hit a 4 iron to three feet on the 16th.
I was quite nervous for my first European Tour event, the 20-year-old said. The eagle took a lot of first-hole nerves away and relieved the pressure.
Matthew Millar (67) was two strokes behind in fourth, and five players were tied at 68, including teenager Rory McIlory. Two-time Masters champion Jose Maria Olazabal, who was playing in his first tournament after a nine-month layoff because of injury problems, shot a 71.