Zoe Hives has parlayed her Australian Open wildcard entry into the biggest win of her fledgling career.

The 22-year-old Victorian defied her ranking of No.225 in the world to upstage seasoned American Bethanie Mattek-Sands 6-1 6-2 at Melbourne Park on Monday.

Hives earned a second-round crack at French 19th seed Carolina Garcia after joining fellow Australian Astra Sharma as a first-time main-draw winner at the Open.

Sharma earlier outlasted wildcard Priscilla Hon 7-5 4-6 6-1 in a gruelling all-Australian affair on Court 7.

Hon needed medical assistance after the two-hour-and-nine-minute encounter played in oppressive heat.

Hives, Sharma and Hon are among 14 Australians in action on day one.