Kevin Anderson was unable to back up his Flushing Meadows run, edged by Kyle Edmund in a five-set thriller at the Australian Open.
The South African 11th seed reached his maiden grand slam decider at the US Open last year, but he made an early exit in Melbourne on Monday.
Handed a difficult first-round clash, Anderson went down to Edmund 6-7 (4-7) 6-3 3-6 6-3 6-4 in three hours, 59 minutes.
It marked Anderson's sixth first-round exit in 10 appearances at the year's opening grand slam.
Edmund, who hit 61 winners in his victory, is into the second round at the Australian Open for just the second time, the Brit to face Uzbek Denis Istomin.