Chasing 312 to go 2-0 up in the three-match series, India needed 100 runs from the last 10 overs with five wickets in hand.
Patel smashed 64 not out off 35 balls, as his fifth six sealed India’s thrilling victory with two balls to spare.
“It’s very special. It came at a crucial time and also helped the team to win the series,” the 28-year-old said after collecting the man-of-the-match award.
“When I went out, I aimed for 10-11 an over. We thought it could be done because of our IPL experience.
“We just needed to remain calm and keep the intensity up. This is my first ODI (series) after nearly five years. I would want to continue performing like this for my team.”
For the hosts, Shai Hope smashed 115 in his 100th ODI and captain Nicholas Pooran contributed 74 but it was not enough in the end.
Shreyas Iyer and Sanju Samson also scored half-centuries for India but the day belonged to Patel, who also claimed a wicket with his left-arm spin.
Shikhar Dhawan, leading a depleted India side in absence of regular skipper Rohit Sharma, said the IPL experience had prepared them for such high-scoring chases.
“Our domestic and IPL cricket keep us ready … As Axar said, he’s done it multiple times in IPL.”
The teams meet again for the third and final ODI on Wednesday, which will be followed by a five-match T20 series.