With this victory, India colts have assured their place in the final to be played on December 19.
Chasing 222, India lost their openers early but Sundar and Anmolpreet Singh put their side back on track with a 55-run partnership.
Anmolpreet was run out for 25 in the 19th over, but Sundar carried onto make 61, before he fell in a similar manner. Virat then sealed the issue in India's favour with an unbeaten 60 off 89 balls.
Sri Lanka lost their last six wickets for 55 runs and were restricted to 221. Seamer Khaleel Ahmed was the most successful bowler for India, returning figures of four for 55.