"It was my first one, I've tried it for so many years," she said.
No. 5 Williams was one of three US women's seed to go down, followed by U.S. Open winner Sloane Stephens (13th) and No. 10 CoCo Vandegweghe.
Stephens continued her dismal form since the New York success four months ago losing, 2-6, 7-6 (7-2), 6-2, to China's Zhang Shuai after failing to serve out a straight-set win.
Zhang fought back as Stephens dropped her eighth match since winning the final at Flushing Meadows, exiting for the third consecutive year in the first round in Melbourne.
Vandeweghe lost to Hungarian Timea Babos, 7-6 (7-4), 6-2, with American drawing a penalty for wasting time by arguing with the chair umpire about the late arrival of energy-sustaining bananas to the court.
Second seed Caroline Wozniacki got away to a winning start, beating Romanian Mihaela Buzarnescu, 6-2, 6-3.
"I'm happy to be through. It was not an easy match," Wozniacki said. "Maybe on paper it looks easy, but it wasn't. She's a tricky lefty opponent with a lot of confidence. I feel pretty good. I think it's a good start. Hopefully I can progress from here."
Seventh seed Jelena Ostapenko won a battle between current and former Roland Garros champions as the Latvian defeated Italian veteran Francesca Schiavone, 6-1, 6-4.
The 37-year-old Schiavone claimed the Paris title in 2011 and only recently reversed a decision to retire.
Ostapenko said she overcame problems with her game in the second set to move ahead at Melbourne park.
"I was playing pretty well. I started the match very, very well. Losing the second set 4-1, but then I came back. I'm happy the way I played," she said.
"I started to miss more in the second set but I found my game. I'm glad with how I finished the match."
German 12th seed Julia Goerges continued a winning streak going back to last October, defeating Sofia Kenin of the U.S., 6-4, 6-4.
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