Before the World Cup there were concerns around his form as he bumbled his way through the seven-match lead-up series against Sri Lanka. The 28-year-old passed 50 only once against a poor Sri Lankan bowling attack and three ducks were worrying.
It followed on from a middling 2014 when he averaged 30 but his strike rake dipped below 70 as he struggled to push singles and the dot balls mounted.
But his recent work with former New Zealand great Martin Crowe has paid off.
"Mainly footwork stuff and lining up the bowlers a bit better than what I had been," Guptill said of Crowe's advice. "Trying to hit the ball a little straighter, instead of trying to play too square, too early, and that's been the main thing. I think it's working pretty well at the moment."
When he brought up his double century - becoming the first New Zealander to do so in an ODI - Guptill pointed his bat to towards the team dugout, removed his helmet and let out a roar.
The Aucklander was dropped at square leg in the first over by Marlon Samuels when he had only four runs to his name - cricket can be an unforgiving sport.
"Obviously there's pressure but you've just got to try and put it behind you and just watch the ball as hard as you can and play it accordingly," Guptill said.
The 30,268-strong crowd chanted his name as his innings progressed and his show-stopping performance secured him the second-highest one-day international score of all time.
The West Indies bowlers dropped their heads as they couldn't find anything that resembled a good length and Guptill had a bat as his weapon and an eye that couldn't miss a trick.
His innings spanned 225 minutes, included 24 fours and 11 sixes. It was the seventh century of his ODI career. But the most significant by some margin.
Among the records to tumble:
-Guptill now owns the second-highest ODI score of all time, trailing only Rohit Sharma's 264 last year against Sri Lanka.
-He posted the highest score ever by a New Zealander, surpassing his own 189 not out against England in 2013.
-Guptill's knock beat Glenn Turner's 171 not out against East Africa to be the highest score by a Kiwi at a World Cup.
-He is just the sixth man in history to score a ODI double-century.
-He became the first player to score more than 150 in a World Cup knockout game, with Adam Gilchrist's 149 the previous mark.
