Playing at the different venue due to a change notified five hours before the kick off, Pune FC were handed their first loss of the competition as Azaharuddin Mallick (32nd, 62nd & 76th minute) and SK Azaruddin (83rd) struck for the home side.
Pune FC played almost the entire second half with a man less after skipper Altamash Sayed was sent off in the 49th minute.
Playing their second game in as many days, Pune FC Coach Naushad Moosa made six changes to the squad.
Ten minutes later, winger Sannik Murmu went agonisingly close. The youngster dribbled past three defenders to get into the box but his attempt was saved by the custodian.
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As Pune FC pushed forward, United SC capitalised on the counter attack and took the lead on a breakaway move in the 32nd minute. Mallick ran solo and finished off with a good shot to give the home a one goal advantage.
After the interval, Pune FC were hit hard when Altamash was sent off four minutes after restart. The skipper was elbowed by an opponent and reacted instinctively which was noticed by the referee who flashed a direct red card.
Thereafter, Pune FC were forced to chase the game with ten men in sweltering heat as United SC preferred to hold back and move ahead on counter attacks.