When the Australian rolled in an 8-footer for birdie at the 14th hole to move four strokes clear of the field he also became just the second player in major championship history to reach 20 under par.
Tiger Woods was briefly at 20 under par at the 2000 Open Championship but finished that event at 19 under.
“I had no idea about the record until after it was over and someone told me about it,” said Day, who finished three strokes clear of Jordan Spieth. “The amount of history that's been through our game, in our sport, to be able to hold that record currently is really amazing.”
Day bogeyed the 15th hole to slip back to 19 under, but he quickly rebounded with his final birdie of the event with a two-putt par at the 16th hole and finished at 20-under 268.
“There's been so many fantastic golfers throughout the history of our sport and playing so many major championships, but for me to be able to get to 20 under par and hold that record, I mean, some of the names I never thought I would be able to put my name with,” Day said.