Chasing a target of 201, the Indians got the required runs in 39.2 overs to not only garner the five winners' points, but also bag a bonus, thereby boosting their points tally to 13.
The men from the emerald islands are on 10 points from three matches, while Pakistan have culled a solitary point from two outings.
The Sri Lankans, who batted first on winning the toss, found the Indian bowling too hot to handle and folded up for 200 in 47 overs.
In reply, India 'A' lost Sanjay Bangar (15) and Mohammed Kaif (0) early on, before Badani and opener Gautam Gambhir (51) added 85 runs for the third wicket to swing the game in India's favour.
In-form batsman Gambhir continued his fine show to notch up his third 50 plus score in the tournament in as many innings. He earlier had 113 and 82 in the first two matches.
Badani, who had not been able to found his touch so far, decided to prove his detractors wrong with a fine innings, embellished with spectacular shots. He hit eight fours and a six. Once Gambhir departed, Yuvraj Singh (33 not out) joined Man of the Match Badani and the two remained unseparated with a 71 run stand for the fourth wicket to carry India through to victory with ten balls to spare.
In the morning, the Indian bowlers came up with a fine performance to restrict Sri Lanka, whose batsmen had gone on the rampage in the first two matches, to a modest total.
Struggling at 39 for three, the visitors were rescued by a fine 85 run fourth wicket partnership between opener S Jayantha (65) and Naveed Nawaz (57). But once they left, the other batsmen failed to come to terms with the slow pitch and the Indian attack as the visitors innings folded in 47 overs.
The day began sensationally with Sri Lanka losing S Kalavitigoda (0) and Jehan Mubabarrak (0) inside the first four overs, but they got the biggest blow when skipper Russel Arnold (9) got out for the first time in the tournament in the first ball of the 13th over.
Arnold, who scripted Lanka's triumph against both India and Pakistan in the earlier matches, has now totalled 205 runs in the tournament. His average stands at a monumental 205.
Jayantha completed his 50 in the 22nd over off 62 balls, before he tried to sweep S Bahutale and holed out to Dinesh Mongia at deep square leg.
A little later, Nawaz got his second 50 of the tournament in great style, as he lifted Bahutale over long off to move from 48 to 54. However, he was adjudged leg-before to Sarandeep Singh soon after.
Bangar three for 43 finished as the most successful Indian 'A' bowler with Bhandari, Munaf Patel and Sarandeep Singh picking up two wickets each.
Bhandari steals the show as India beat Pak