Dhoni (119 not out) and Gambhir (79), who had scored big hundreds during the 121-run victory over the archrivals in the previous clash, put together 169 runs for the second wicket as Indians overhauled the Pakistani target of 235 runs with five overs to spare.
India 'A' has already been ensured a berth in the final after winning all the league matches after their surprise loss to Kenya in the opening tie.
On the other hand Pakistan 'A' has just one win under their belt from five outings and face a do-or-die match against hosts Kenya who have two wins from as many matches.
Dhoni, who has been knocking on the doors of the national side with his consistent batting, hit nine fours and five sixes in his 134-ball knock.
The Indians did not have a great start as they lost opener Dhiraj Jadhav with just eight runs on the board. Dhoni and Gambhir then played cautiously and ensured that there were no more hiccups before opening out in the later part of the innings.