With the great mates drawing each other Australia was always guaranteed another player joining its top female player Sam Stosur in round two with Duckworth prevailing 6-4 7-6 (10-8) 4-6 5-7 8-6.
The 20-year-old Sydneysider took a two-set lead but then allowed Mitchell, also 20, back into the match.
Cheered by a full-house on showcourt two at Melbourne Park on Tuesday, Duckworth led 4-2 in the decider but Mitchell, from the Gold Coast, broke back to take the match down to the wire before it was decided in four hours and 26 minutes.
Earlier, fellow young Australians Luke Saville and John-Patrick Smith bowed out in the first round.
Saville joined the growing list of local losers by falling 6-7 (4-7) 6-3 6-2 6-3 to world No. 73 Japan's Go Soeda while fellow Queenslander Smith succumbed to Portugal's Joao Sousa 6-4 6-1 6-4.