Defending champion Czech Jiri Lehecka pulled out, citing fatigue.
Lehecka on Sunday night won the Brisbane International, his second ATP title, when American Reilly Opelka quit due to a back injury inside 15 minutes of the final.
Lehecka's countryman and Adelaide third seed Tomas Machac also was a late scratching in South Australia.
A left knee ailment forced Machac out of a lead-in tournament to the Australian Open starting on January 12 in Melbourne.
The Adelaide field is headlined by home-town hero Thanasi Kokkinakis, who plays Japan's Yoshihito Nishioka on Monday night.
America's world No.12 Tommy Paul is top seed in Adelaide.
Walton and Duckworth advanced to the main draw after winning all-Australian duels in the final phase of qualifying.
Duckworth downed wildcard Jacob Bradshaw 6-2 6-2, and Walton secured a comeback 1-6 7-6 (7-4) 6-4 win over Rinky Hijikata.
In Monday's sole men's first-round fixture ahead of evening and night matches, Canada's Denis Shapovalov upset China's ninth seed Zhizhen Zhang 6-3 6-4.
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