The Queensland native broke through for his first major title in August 2015, winning the PGA Championship at Whistling Straits by three strokes over Jordan Spieth. It was one of five victories in 2015 by Day, who overtook Jordan Spieth as the No. 1-ranked player in the Official World Golf Ranking. He won three times in 2016: the Arnold Palmer Invitational, the WGC-Dell Match Play and The Players Championship, joining countryman Greg Norman and Tiger Woods as the only No. 1-ranked golfers to win that event. Day, who owns 12 PGA Tour titles, represented the International Team in the 2011, 2013, 2015 and 2017 Presidents Cups. He also owns five top-10 U.S. Open finishes, including a solo second in 2011 and a tie for second in 2013.
U.S. Open Record
| Year | Site | Scores | To Par | Finish |
| 2020 | Winged Foot Golf Club (West Course) | 72-74-76-72--294 | +14 | T-38 |
| 2019 | Pebble Beach Golf Links | 70-73-70-69--282 | -2 | T-21 |
| 2018 | Shinnecock Hills Golf Club | 79-73 | +12 | MC |
| 2017 | Erin Hills | 79-75 | +10 | MC |
| 2016 | Oakmont Country Club | 76-69-66-71--282 | +2 | T-8 |
| 2015 | Chambers Bay | 68-70-68-74-280 | E | T-9 |
| 2014 | Pinehurst Resort & C.C. (Course No. 2) | 73-68-72-68--281 | +1 | T-4 |
| 2013 | Merion Golf Club | 70-74-68-71--283 | +3 | T-2 |
| 2012 | The Olympic Club | 75-71-76-73-295 | +15 | T-59 |
| 2011 | Congressional Country Club | 71-72-65-68--276 | -8 | 2 |