Crowe, who is battling terminal cancer, also tipped another of his proteges Ross Taylor to come good for the Black Caps, who face South Africa on Tuesday for a spot in the final. (Preview)
Guptill hit a World Cup-record 237 not out as New Zealand crushed the West Indies by 143 runs on Saturday, the second-highest individual score in one-day international history.
After the 163-ball knock, the opener revealed that tips from Crowe had helped improve his batting, particularly his footwork and stance.
But Crowe said Guptill deserved the credit for being prepared to ask for help, then going back to the basics to alter his technique.
"It's a courageous move to rebuild at 28," Crowe told Fairfax New Zealand. (World Cup 2015 Semi-finals, SWOT Analysis of Team New Zealand: The Kiwis Set to Fly into the Finals)
"He wants to be a successful Test batsman and he made the right call at the right time."
Crowe said he sent Guptill a text message reading "OMG" after his innings, although he said it did not carry the standard meaning of "Oh My God". (Guptill, Not History Counts for Kiwis, Says McCullum)
"(It) could also be read as 'Oh Marty Guptill' but actually it meant 'Oh My Gap'," he said. (Kiwis, Proteas Rule Out Sledging)
"We've talked a lot over the last few months about not looking at fielders, about looking at gaps. The more the mind is focused on gaps the more it will find them."
Crowe, who was inducted into the ICC Hall of Fame this month and is widely regarded as New Zealand's greatest ever batsman, also backed Taylor to shine.
The ex-captain struggled early in the tournament but has scored 42 and 56 in his last two innings and Crowe, who has mentored Taylor throughout his career, was confident the player was coming out of his slump.
"He's made the adjustments for this tournament and let's hope he can really express himself at the back end," Crowe told Fairfax. (No One Can Stop Us, Says De Villiers)
"I think he has had enough time in the middle now to express himself. The whole point is to peak at the back end and I think he can nail it."
Crowe led New Zealand to the semi-final of the 1992 World Cup. He retired in 1995 and in October 2012 revealed he had lymphoma.