Devastated after conceding 99 runs in less than eight overs towards the end, which helped the hosts set a daunting target of 316, the West Indians were all out for 191 in 43.5 overs.
Such was the onslaught by Nath and Kumar Deobrat (37 off 16; 2x4, 3x6) that India, from 216 for two in the 43rd over, raced to 315 by the end of innings.
Aparajith, after contributing a handy 42, returned impressive figures of four for 38.
Opting to bat after winning the toss, the Indians were off to a disastrous start as they lost opener Manan Vohra with nothing on the board.
However, skipper Unmukt Chand (66 off 79 balls) along with Hanuman Vihari (68 off 88) led a strong Indian fightback, sharing 143 runs for the second wicket in 27.5 overs at the Port Trust Diamond Jubilee Stadium.
Before Chand was removed by Donovan Nelson, he had hit six boundaries and two sixes to wrest the initiative.
Merely three balls later, Ronsford Beaton got the better of Vihari, but not before the batsman had hit nine boundaries.
The show then belonged to Nath who, despite the team losing suffering two quick blows, looked at ease.
Pacing his innings to near-perfection, Nath struck four boundaries and as many sixes during his stay at the crease.
Assisting Nath in his quest to bat the opposition out of the match, Aparajith was involved in a 71-run stand for the fourth wicket in 14 overs. However, it was Nath's association with Deobrat that left the opposition looking cover.
Chasing a stiff target, the West Indies batsmen crumbled under the pressure created by Aparajith. Shreyas Gopal and Vikas Mishra finished with two apiece.