China's Sun Yang reacts after men's 400m freestyle final of swimming at the 2016 Rio Olympic Games in Rio de Janeiro, Brazil, on Aug. 6, 2016. Sun Yang won the silver medal with 3 minutes 41.68 seconds.（Xinhua/Liu Dawei）
Mack Horton clinched Australia's first gold medal of the Rio Olympics by upsetting favorite Sun Yang of China in the men's 400m freestyle final on Saturday.
Horton clocked 3 minutes 41.55 seconds, eclipsing Sun by just 13 hundredths of a second at the Olympic Aquatics stadium. Gabriele Detti of Italy was third in 3:43.49.
Mack, who finished second fastest in qualifying, is competing at his first Olympic Games in Rio. The 20-year-old was the bronze medalist in the 800m freestyle at last year's world championships in Kazan.
Sun was the pre-race favorite, having won gold in the same event at the London 2012 Games. The 24-year-old is also the defending 1500m Olympic champion.
