The Proteas outclassed the defending champions by 187/7 to 111, with Miller's 63 off 35 and Dewald Brevis' 45 off 29 powering the chase.
Miller said the key was clarity of thought and disciplined execution, focusing on taking the spinner down and sticking to basics. He praised the team's maturity and said India are beatable when the Proteas stay in their lane.