KL Rahul and Shikhar Dhawan both hit fifties to lay the foundation for India’s imposing total of 201-6 after being put into bat at the Maharashtra Cricket Association Stadium.
Sri Lanka’s top order wilted early in their reply and Dhananjaya de Silva’s counter-attacking 57 was not enough as they were bundled out for 123 in 15.5 overs.
Saini, who took 2-18 in the second match, led the rout claiming 3-28, while Thakur grabbed two wickets to go with his 22 not out off just eight deliveries.
Earlier, Dasun Shanaka dropped Dhawan in the second over and his team paid for the costly mistake as the left-hander went on to forge a 97-run partnership with Rahul.
Left-arm spinner Lakshan Sandakan (3-35) separated them when he dismissed Dhawan for 52 and wickets suddenly started tumbling.
Sandakan dismissed Rahul (54) and the in-form Shreyas Iyer in the same over, while Virat Kohli and Washington Sundar departed in successive deliveries.
Manish Pandey (31 not out) and Thakur made sure the collapse did not really matter as they took India past the 200-mark.
Sri Lanka needed a strong start to stay in the chase but the Indian quicks blew away their top order, reducing them to 26-4 in the sixth over.
The 68-run stand between de Silva and Angelo Mathews (31) was the lone significant partnership in the Sri Lankan innings.
The series opener in Guwahati was abandoned because of rain and India romped home by seven wickets in the second match in Indore.