Ashwin grabbed 5 for 52 in 16 overs en route his 18th five-wicket haul in longer format as West Indies were all-out for 196 in 52.3 overs.
The off-spinner took centrestage after initial breakthroughs from Ishant Sharma (2/53 in 10 overs) and Mohammed Shami (2/23) as rival skipper Jason Holder had decided to make first use of a lively pitch.
The visitors then further consolidated their position by reaching 126 for 1 as they are now only 70 runs short of the West Indies first innings score.
Rahul's innings had 10 boundaries in 114 balls as he added 87 runs for the first wicket with a subdued Shikhar Dhawan (27, 52 balls, 5x4). Giving company was Cheteshwar Pujara batting on (18 batting).
More From This Section
Earlier, in the West Indies innings it was Jermaine Blackwood, who showed some counter-attacking instincts with a run-a-ball 62 that had seven fours and four sixes. Along with Marlon Samuels (37, 88 balls), Blackwood added 81 runs for the fourth wicket after the Caribbeans were reeling at 7 for 3 with Ishant and Shami polishing off the top-order.
Ashwin now has 188 victims in 34 matches. He also has the disticntion of four five-wicket hauls in successive matches. He is only the third Indian spinner to do so after Bhagwat Chandrasekhar and Anil Kumble.
The slide in the post-tea session began when Samuels starting to attack, was fooled by Ashwin's flight lobbing a simple catch to KL Rahul short-leg.
Six overs later, Shane Dowrich (5) edged one behind from the toe-end of his bat, the batsman in half mind whether to leave or play at the ball.
(REOPENS FGN 1)
The off-spinner celebrated his second successive five-wicket haul in the series two overs later then, as Jason Holder (13) was out caught bat-pad at forward short leg.
At the stroke of tea then, Amit Mishra (1-38) wrapped up the West Indies' innings, but not before Miguel Cummins (24 not out) and Shannon Gabriel (15) threw their bats around to add 38 runs for the last wicket.
This was after West Indies won the toss on a damp pitch and elected to bat. They made one change to their line-up, bringing in debutant Miguel Cummins in place of Carlos Brathwaite, while India were forced to make a change as well. KL Rahul came into the side in place of the injured Murali Vijay.
Ishant and Shami then started proceedings for India, and the two bowlers were right on the money from the word go. The former in particular was impressive with his line and length, a marked improvement from the Antigua Test, as he pitched the ball further up and got it to move about.
Off the very next ball, Darren Bravo (0) was forced to fend an incoming delivery and skipper Virat Kohli completed a brilliant diving catch at second slip.
Three overs later, Shami got Rajendra Chandrika (5) to drive, only to find KL Rahul at gully as West Indies were struggling within the first 30 minutes of play.
Spin was introduced in the 12th over as Ashwin came on,
Samuels continuously egged him on at the other end. He played some attacking shots as well, including a cut six off Umesh Yadav (0-30), though he was tight enough in his defence too.
It seemed as there was a continuous barrage of sixes, five of them coming in this first session of play, four from Blackwood alone as West Indies raced past the 50-mark in the 16th over despite their poor start. Their 50-partnership had come off just 75 balls, and in doing so Blackwood reached his 7th Test fifty off only 47 balls.