He won the PGA Championship at Whistling Straits and set a record as the first player to finish a major at 20 - under - par .
Australian Jason Day broke through in 2015 with his first major championship .
Jason Day won the PGA Championship at Whistling Straits and set a record as the first player to finish a major at 20 - under - par .
Australian Jason Day broke through in 2015 with his first major championship .