Mizoram were already out of contention, having lost their first two matches. Delhi finished with three points from as many draws. Bengal and Tamil Nadu thus advanced to the last four from this group, joining Goa and Punjab.
In the late match of the day, Tamil Nadu struck a late goal to shock Bengal 2-1 in their final quarterfinal league match and thereby topped Group B. In a match that saw a 25-minute stoppage early in the second half because of a power-trip, Nilendra Dewan put Bengal ahead, while VR Murugappan and PC Riju scored for the visitors to help them notch a grand win. Last year's semifinalists Tamil Nadu thus finished with seven points and will take on Punjab in the second semifinal on Friday.
Bengal, on the other hand, have the tougher assignment of facing Goa in what will be a rematch of last edition's final, which the hosts lost via tie-breaker.
Wednesday evening's clash, reduced to just a battle to identify the group winners after Delhi bowed out following a draw with Mizoram earlier in the day, kicked off at a furious pace with both sides looking to play an attacking game.
Bengal had the better of early exchanges and could have gone ahead in the fifth minute when Denson Devadas glancing header off a Snehashish Chakraborty free-kick from the left came off the upright.
It was not long before the Shabbir Ali-coached side surged ahead. Midfielder Jayanta Sen played a pass on the right channel of the box in the 16th minute, which was nicely converted by Dewan with a diagonal grounder to the far post.
Bengal's lead didn't last beyond a minute. Murugappan, receiving a long ball in the Bengal penalty area, finished off clinically with a right-footer past approaching Bengal custodian Sandip Nandy.
Bengal had the chance to regain the advantage towards the end of the first half when Gouranga Datta, following a clearance off a corner kick, crossed towards the goalmouth for an unmarked Dewan.
But the youngsters faulty receiving gave Tamil Nadu goalkeeper A Arun Pradeep enough time to avert danger. Five minutes into the second half, the stadium plunged into darkness one more time.
Though power was back within seconds, the lights took time to take full effect, thereby resulting in the stoppage.
Bengal had a golden chance to seal the match soon after resumption when Shankar Oraon was served with a fine ball inside the box by Gouranga, but the former hit the side-netting. In the 71st minute, Dewan failed to chip a long ball over the goalkeeper.
Riju made Bengal pay dearly for the misses, scoring against the run of play. He played a wall pass with substitute M Elamurugan to barge into the box before skillfully beating the onrushing Bengal goalkeeper with an outside dodge and placing it home.