A second half strike from Baldeep Singh saw United SC beat Pune FC 1-0 in a Group A encounter of the 35th Federation Cup at the Jawaharlal Nehru Stadium in Kochi on Friday.
It was a must-win game for both sides but in the end the Kolkata side triumphed to remain in contention for a semi-final place.
The first half saw very little goalmouth action as neither side created too many openings.
United SC's best chance of the half fell to Dhananchandra Singh who couldn't hit the target despite getting a free header from an Eric Brown cross.
Mike Snoei replaced James Meyer with Gabriel Fernandes at the interval but that substitution didn't really change Pune's fortunes as they struggled to create chances from open play.
United SC then suffered a blow as Ranti Martins went off with an injury and was replaced by Baldeep Singh.
The deadlock was finally broken by United SC when Eric Brown went past Othallo Tabia on the left and found Baldeep (71st) in the area and the substitute scored past Amrinder.
In Manjeri, second half goals from Josimar da Silva (75th) and substitute Rakesh Masih (90+2) kept alive Mohammedan Sporting's semi-final hopes as they downed lowly Bhawanipore FC by two goals in a Group D match.
Josimar scored off Manish Maithani's corner after Nabi fed the ball for the Brazilian inside the six-yard area.
Mohammedan Sporting saw their lead getting doubled deep into second half stoppage time as substitute Rakesh Masih sent home a splendid left-footed long ranger that dipped into the net
It was the Durand Cup champions who set the pace early on in the first half. Winning three corners in the first twenty minutes, the Kolkata outfit kept their city rivals' defense on tenterhooks.
Midfielder Nabin Hela showed sparks of brilliance making space for himself amidst a sea of legs and teeing up Josimar and Penn on most occasions.
The second-division side did not trouble Mohammedan Sporting at all after that and were insipid throughout the match.
Mohammedan Sporting have three points from two matches while Bhawanipore are out of the competition having failed to register a win in their two outings.