Dempo paid for their profligacy with an own goal by their captain and went down 2-3 to Sur Club of Oman in an AFC Cup Group A thriller in Nizwa, Oman.
The I-League champions, who beat Lebanese powerhouse Al Ansar in their opening pool match, wasted a couple of clear chances and conceded an own goal by star playmaker Climax Lawrence at Nizwa stadium, 150 km from Muscat.
Sur took the lead through Daouda Traore in the eighth minute, but Dempo levelled through Nigerian striker Ranti Martins in the 26th. Brazilian Roberto Silva fired the visitors ahead in the 62nd minute only to see Mamoudou Camara level in 69th minute.
Just as the two sides looked set to take a point each -- a result that would have made Dempo coach Mauricio Afonso happy -- Lawrence, who wore the captain's armband instead of Martins in Tuesday's match, dumped a Jose Estefane's strike into his own goal in the 80th minute.
The result leaves Bahrain's Al Muharraq on top of Group A with four points after they drew with Al Ansar. They had earlier beaten Sur 3-2 in their first match.
Dempo and Sur are tied on three points but the Goan side is second due to a better goal difference.
Sur got the lead when Ivory Coast striker Daouda Traore latched on to a long ball and beat goalkeeper Abhijit Mondal from inside the box.
Dempo almost got themselves back on equal terms three minutes later when Martins put the ball home but the referee ruled that he had handled the ball.
Down by a goal, the visitors applied pressure on the hosts and created a couple of chances only to see Martins and his strike partner Chidi Edeh fail to finish the moves.
Chidi shot over the crossbar from close range after some good work by him and Martins.
Repeated Dempo onslaughts, however, paid off when an unmarked Martins header found the back of the net from a Nicolau Borges free-kick.
After the breather, Dempo continued to attack and hardworking Brazilian midfielder Roberto Mendes Silva scored following a neat interplay with Martins.
Martins could have increased his side's lead but his shot was cleared off the goal-line by defender Ali Al Farsi.
Sur came back into the match when Mamoudou Camara fired a low shot which beat custodian Mondal.
Ten minutes from the long whistle, Dempo's hearts were broken when a Jose Estefano's shot deflected towards the goal and Lawrence put the finishing touches.
Despite the loss, Dempo coach Mauricio Afonso praised his boys for their valiant fight.
"We played a good game and I'm satisfied with the performance of the players. Sur are a strong team and it wasn't going to be easy to beat them.
"We were better in the first half and had several chances but we couldn't convert them into goals," he said, ruing the missed chances.
"Our next match against Al Muharraq is very important and we can't lose if we want to remain in contention. We must not drop any more points," Afonso said.
Sur's Tunisian coach Ahmed El Akhdar was relieved to collect their first points in the competition.
"It is great to win such a difficult game. It was not easy for us because we had no idea about our opponents and the pitch at the stadium is not that good," said El Akhdar.
