Dudu Omagbemi and Konstantinos Katsouranis struck either side of the break as FC Pune City capped an outstanding 3-1 away win against Atletico de Kolkata to snap the league leaders unbeaten run in the ISL here.
However ATK still remained on top with 12 points.
The Pune franchise, who travelled without their French World Cup winner David Trezeguet, stunned one and all as their East Bengal recruit Dudu repaid his coach's faith with a well directed header in the 31st minute to silence the crowd.
Till then, ATK who were bolstered by the return of mercurial forward Fikru Teferra and manager Antonio Habas off the field impressed with their passing and had the better share of possession against Pune's defence that looked weak.
But the day clearly did not belong to the league leaders who had two howlers early on with their top two striking duo -- Fikru and Borja Fernandez -- missing one each.
Having seized the momentum thanks to Nigerian's strike, Kostas Katsouranis made it 2-0 after the break when the Greek World Cupper used his outstep to curl one away as goalie Subhasish Roy Chowdhury looked in absolute disbelief.
ATK finally made their presence in the scoresheet in the 84th minute after Pune goalkeeper Arindam Bhattacharya felled Fikru in an inexplicable manner as the Ethiopian converted from the spot without much fuss.
Pune got a free-kick at the edge of the box when Josemi pushed Dudu from behind as Davide Colomba converted the shot with a leftfooter that took a Kingshuk Debnath's deflection to hit the back of the net to sink ATK's fortunes. Pune might not have the best of defence on display but they survived with ATK's sluggish approach in the first-half.
When it was expected that the team would put up a spirited display with mercurial Fikru back up front and an animated coach Habas back in his dug-out, ATK's approach was a bit casual.
In the very first opportunity, Fikru received the ball from Ofentse Nato as the Ethiopian striker turned and volleyed from outside the box, but only to shoot it wide of the goal in the 11th minute.
After Fikru, it was the turn of another top ATK player as Borja Fernandez after getting the ball from Cavin Lobo from the left-flank could only shoot over the post much to everybody's surprise.
ATK could have been down by two goals at the break but Subhasish Roy Chowdhury brought up a spirited save diving towards his right from a John Goossens strike.
ATK had another setback when their top defender Jose Miguel had a bloody chin but the Spaniard played on.