Saini bowled with searing pace on Tuesday and troubled the Lankan batsmen to return superb figures of 2/18 in four overs as India restricted Sri Lanka to 142/9 after choosing to field first.
The batters then did the job with ease as India won with 15 balls to spare, scoring 144/3 in 17.3 overs.
"When I made my T20I debut, I wanted to bowl fast, but now I know the importance of the slower deliveries," he added.
"I practiced well and was confident. It's important to be confident and it's also important to use the variations. I was more happy to take a wicket with the yorker (Danushka Gunathilaka)," he said on the match.
Saini has so far played eight T20Is and one ODI for India.