The Englishman fired seven birdies which was matched by his equally impressive Ryder Cup team-mate McDowell at the West Course.
Malaysia's Danny Chia also had a tale to tell, as he held on to his game strongly with a 67 to tie for third with Englishman Tommy Fleetwood and South Korean Kang Sung-Hoon at the US$3 million event sanctioned by the Asian and European Tours.
Westwood put himself in strong position to win the Maybank Malaysian Open for a record-equalling third time after displaying another dominant performance at a venue where he won by seven shots last year.
“I’ll take that. I putted very nicely and started the ball on line well. I left a couple short in the middle when I was fooled by the grain, but overall I’m very happy. It’s probably the toughest I’ve ever seen this golf course play,” said Westwood.
And he only had the win to battle with in the first round as he found the course in similar condition like last season.
"It’s (the course) is in very similar condition. The wind just made it that little bit harder – not the fact it’s blowing particularly hard, but that it’s changing direction. It gets very confusing,” added the Englishman, who is ranked 30th in the world.
McDowell, playing in the Maybank Malaysian Open for the first time since 2008, kept his emotions under control on a humid day. He made only one bogey on the par four sixth hole but battled into contention with two birdies in his closing three holes.
“This morning I was really trying not to over-react to any mistakes I made. It really is too hot to get mad out there, so you have to keep your emotions under control and obviously stay hydrated and cool and try to embrace it,” said McDowell.
Playing in only his second event in 2015, the Northern Irishman fancies his chances of winning his first title this year.
“I work off the course over the winter improving some things physically and in my swing, and things seem to be clicking really well. It is early days, but I’m feeling relaxed and my attitude’s good too. If I can continue that for the rest of the year then good things will come,” he added.