The 20-year-old was second over eight lengths at the World Championships in Shanghai last year before producing a sublime 1500m Freestyle in which he lowered Grant Hackett's long-standing world record.
He qualified fastest from a dramatic morning session which had seen defending champion Park Tae-hwan disqualified and then reinstated.
Republic of Korea's Park was second in the showpiece, with Peter Vanderkaay of USA third.
Meanwhile, Ye Shiwen, just 16, secured China's second gold of the session and also the first long-course world record set by a woman since the ban on performance-enhancing suits in the women's 400m Individual Medley.
Ye, who won the 200m Individual Medley aged 15 at the World Championships in Shanghai last year, produced a superb Freestyle to stretch away and touch in 4:28.43.
World champion Elizabeth Beisel was second, with Ye's compatriot Xuanxu Li third.
Then, in the final race of the night, there was joy for Australia when they won the gold medal in the women's 4 x 100m Freestyle Relay final with an impressive victory.