The 23-year-old Lau drained a clutch 12-foot birdie putt on the final hole at Thirteenth Beach on Sunday to sign for a six-under 66 and get to 12-under 277.
But with defending champion and former world No.1 Jiyai Shin still out on the course, victory was far from assured.
After finding trouble off the tee, the great South Korean - a winner of 64 pro tournaments around the globe - hit a clutch three-wood onto the 18th green, only to see her brave birdie attempt lip out from 30 feet.
Not that Lau was able to watch.
"Jiyai was on the last hole, a guy kept updating me where she was hitting it and I was like 'you know, I can't do this'," said the Malaysian.
"I was super nervous. I'd never felt this nervous before, so I took a walk and went to talk to my friend, and that helped a lot."
Those nerves were finally calmed when Lau was informed that Shin had just missed the putt.
Shin (69) finished in outright second at 278, a shot clear of countrywoman Jeongmin Cho.
Karis Davidson (73) and Sarah Jane Smith (71) were the leading Australians in a tie for fifth at 282.
After starting the final day tied for the lead with Shin, Davidson looked well placed for victory, but her challenge petered out with three bogeys in the final 10 holes.
Lau did Years 11 and 12 at Hills International College in Brisbane, a school whose former pupils also include Jason Day.
She then went to the US and enjoyed a stellar college career at the University of Michigan.
After finishing third and second in the previous two weeks on the Australasian WPGA Tour, Sunday's Vic Open triumph was the first of her professional career.
"Malaysia has always been my home, but I have always called Australia my second home, and now the States is obviously my second home as well," Â Lau said.
"Australia holds such a special place in my heart and has done since high school.
"It's just so nice to be back after seven years, seeing a lot of old faces again and old friends."
Seven-time major winner Karrie Webb had a good weekend, finishing in a tie for 11th at two-under after closing with rounds of 67 and 70.
The former world No.1 - who will be the non-playing captain of the Australian women's team at the Paris Olympics - has only teed it up occasionally on the professional stage in the past few years.
