The off-spinner claimed three wickets in his first seven deliveries and finished with 4-8, best by an Indian bowler in this format, as Sri Lanka folded for 82, their lowest total in Twenty20 Internationals.
Chasing the small target, India romped home with 6.1 overs to spare to seal the series 2-1 at Visakhapatnam’s ACA-VDCA Stadium.
Opener Shikhar Dhawan topscored for the hosts with an unbeaten run-a-ball 46 but it was Ashwin’s guile that laid the foundation for India’s comprehensive victory.
Put into bat, Sri Lanka got off to a nightmarish start with Ashwin opening the attack for India.
The spinner drew Niroshan Dickwella forward with his third delivery to get him stumped before trapping Tillakaratne Dilshan leg-before wicket with the sixth.
The wily spinner struck another blow with the first ball of his second over when rival captain Dinesh Chandimal holed out in the deep.
Sri Lanka’s first 21 runs cost them their top half and only Dasun Shanaka (19) and Thisara Perera (12) managed double digit scores in their abject batting capitulation against the Indian spinners who claimed seven of the 10 wickets.
To make it worse for them, the tourists were also handed out a couple of poor decisions with Asela Gunaratne and Sachithra Senanayake given caught out even though replays did not suggest any contact between bat and ball on either occasion.
Defending the paltry score, Dushmantha Chameera dismissed Rohit Sharma for 13 but Dhawan and Ajinkya Rahane (22 not out) steered India to victory to ensure they remain the top ranked team in this format.
Ashwin, who claimed nine wickets in three matches, grabbed both man-of-the-match and man-of-the-series awards.