Praise poured in for Day after the 27-year-old Australian held off the challenge of American star Spieth to win the US PGA Championship at Whistling Straits, the biggest title of his career.
Day carded a final-day 67 to finish on 20 under par and three shots clear of runner-up Spieth, who may have fallen just short in his bid for a third major of the year but still replaced McIlroy as world No 1.
Day’s place in the record books is shown by the lowest winning tiotal in relation to par at major events:
20 under - Jason Day, US PGA (2015)
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19 under - Tiger Woods, Open (2000)
18 under - Nick Faldo, Open (1990); Tiger Woods, Masters (1997); Tiger Woods, US PGA (2000); Tiger Woods, Open (2006); Tiger Woods, US PGA (2006), Jordan Spieth, Masters (2015)
17 under - Jack Nicklaus, Masters (1965); Ray Floyd, Masters (1976); Steve Elkington, US PGA (1995); Rory McIlroy, Open (2014)
16 under - Tiger Woods, Masters (2001); Phil Mickelson, Masters (2010); Louis Oosthuizen, Open (2010); Rory McIlroy, US Open (2011); Rory McIlroy, US PGA (2014)