Star forward Rampal scored two successive field goals in the 35th and 39th minute after Belarus were put in the lead by their skipper Ryta Batura, who scored in the 24th minute through a penalty corner.
Deepika scored India's third goal in the 42nd minute to take a commanding 3-1 lead while the defenders did well to keep the visitors from scoring in the final quarter to ensure a win.
India won the first and the second games 5-1 and 2-1 respectively. The fourth match will take place on Monday, March 6.
The series is part of India's preparations ahead of the Hockey World League (HWL) Round 2 tournament in Canada in April.