On a tricky Kotla surface with variable bounce, Ashoke Dinda (1-27) removed Gautam Gambhir (0) leg before in the very first over as the India discard was beaten for pace.
Veteran left-arm spinner Pragyan Ojha (1/28) then dismissed Gambhir's deputy Unmukt Chand (13) with a ball that kept low and caught him plumb in-front.
Debutant Risabh Panth (28) looked in flowing touch as he tonked Ojha for a straight six and hit some elegant drives off Dinda.
However young left-hander Nitish Rana (30 batting) continued his consistent form adding 44 runs for the fourth wicket with Milind Kumar (20 batting)
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Earlier, Bengal could not capitalise on their overnight score of 272 for three as they lost their seven wickets in one and half sessions with addition of 85 runs to finish their first innings in 135.5 overs.
The slide started in 96th over when Parvinder Awana (1-55) castled Sudeep Chatterjee (116) after he had hit 12 boundaries. The partnership with Wriddhiman (72) yielded 155 runs.
While Veer Pratap and Aamir Gani contributed 26 each, Bengal couldn't get to 400. Pradeep Sangwan (4-48) was the most successful bowler for Delhi.
Bengal coach Sairaj Bahutule was "disappointed" with batting performance.
"There was a silly run-out (Wriddhiman) and we should have got 450 plus. I am not happy with batsmen's performance but bowlers did a good job. The ball is turning and let's hope we have a good day tomorrow," Bahutule said.
Delhi 1st Innings 100/3 (Nitish Rana 30 batting; Pragyan Ojha 1-28, Ashoke Dinda 1-27, Veer Pratap Singh 1-17).