Alastiar Cook and Jennings started well and gave England the chance of dominating first session.
Ravindra Jadeja pulled things back with the wicket of Cook towards the end of the first session.
Jennings also crouched very low to execute sweep shots with ease against the Indian spinners.
The youngster saw off the early tricky phase and soon displayed good technique against the short ball.
England, who won the toss and opted to bat, handed Keaton Jennings his Test cap.
Keaton Jennings of England with team mates during day 1 of the fourth test match between India and England held at the Wankhede Stadium, Mumbai on the 8th December 2016.
Photo by: Deepak Malik/ BCCI/ SPORTZPICS
Ashwin removed Joe Root soon after the Lunch break.
A superb spell of bowling from Ashwin helped India claw their way back. England reached 288 for 5 at stumps.
Moeen Ali scored his 9th fifty but fell soon after for the same score.
Jennings continued to bat confidently and took on the Indian spinners with ease.
Moeen Ali joined Jennings to build a key partnership for England in the second sesion after Root's exit.
With his third reverse-sweep of the innings, Keaton Jennings reached his maiden Test century.
Ashwin rattled England in the final session with three wickets, including that of centurion Jennings.