Second day's play between Mumbai and HP washed out.
Shahbaz Ahmed scalped two batsmen off successive deliveries as Bengal grabbed four wickets in the final session to put Delhi on the backfoot in their Ranji Trophy Group A match, in Kolkata, on Tuesday.
Resuming the second day on 286 for five, Bengal endured a terrible first session in which Anustup Majumdar was run out for 99. That triggered the collapse.
Bengal innings folded for 318 after losing five wickets inside 12 overs.
The hosts though fought back by reducing Delhi to 192 for six at close on day two, taking four wickets for 58 runs in the final session.
Delhi still trail Bengal by 126 runs.
Aided by two brilliant catches, left-arm spinner Shahbaz dismissed Kshitiz Sharma (9) and Simarjeet Singh (0) off successive balls.
First it was Majumdar who took a low catch at first slip to dismiss Sharma, and then Kazi Junaid Saifi caught Singh brilliantly in his second attempt at forward short-leg to put Shahbaz in line for a second hat-trick.
The rookie Bengal all-rounder had taken a hat-trick in their innings and 303-run win over Hyderabad in their last round match at Kalyani.
"At the moment we look better. There's 14 overs left for the new ball and the conditions will be fresh in the morning. We need to bowl well tomorrow," Bengal coach-cum-mentor Arun Lal said.
With rain forecast for the remaining two days, it remains to be seen whether the match will be completed.
"There's possibility of an outright win, but our main fight at the moment is to ensure three points. Once we get there (get a lead), then you are not so desperate," Lal added.
The day started on a negative note for Bengal as Majumdar, having done all the hard work to rebuild the team's innings from 72/3, fell for 99.
Overnight 94, the 35-year-old Majumdar, eyeing his first century in three years, hit an elegant cover drive boundary off Simarjeet to get to 99.
Singh fed him with away deliveries and all hell broke loose when the Delhi pacer bowled one to his pads, and an impatient Majumdar nudged it to midwicket and ran for a single.
But Hiten Dalal came running in, collected the ball with ease and made a diving throw, straight at the stumps to bring an end to Majumdar's sparkling innings.
It triggered the collapse as his partner Shahbaz, who was 39 overnight, soon threw his wicket away, mistiming Simarjeet to fine leg where Dalal took a regulation catch.
In the last match against Hyderabad, Shahbaz had run himself out for 49.
Simarjeet then ran through the lower order to become the most successful bowler for Delhi with 4/77, while left-arm spinner Vikas Mishra returned with figures of 3/78.
Bengal seamer Nilkantha Das, who made his first class debut at 31, cleaned up Delhi openers Kunal Chandela (nine) and Dalal (40) with yorkers to have them 87/2.
But skipper Dhruv Shorey played beautifully with an array of strokes, while in-form Nitesh Rana, who plays for Kolkata Knight Riders in the IPL, found himself at home to lead the recovery.
Delhi looked rock solid on 147/2 but Mukesh Kumar bowled a sharp in-swinging delivery to dismiss left-hander Rana caught-behind.
Mukesh went on to take the prized scalp of Shorey in addition of just four runs with a late out-swinger to lead Bengal's fightback in the final session.
Bengal (1st innings): 318 all out in 98.4 overs (Anustup Majumdar 99, Shreevats Goswami 59, Shahbaz Ahmed 46, Koushik Ghosh 46; Simarjeet Singh 4/77, Vikas Mishra 3/78).
Delhi (1st innings): 192 for six in 65.3 overs (Dhruv Shorey 65, Hiten Dalal 40; S Ahmed 2/11, N Das 2/36).
Second day's play between Mumbai and HP washed out
Dharamsala: The second day's play in the Ranji Trophy Elite Group B game between Mumbai and Himachal Pradesh was washed out without a ball being bowled on Tuesday.
On the opening day, Monday, Sarfaraz Khan struck an unbeaten 226 to propel Mumbai to a commanding 372 for five.
A morning drizzle first delayed the start of play and later, umpires S Ravi and Vineet Kulkarni, after consultation with curator Sunil Chauhan, called it off at the picturesque HPCA Stadium.
In the last game against Uttar Pradesh, Sarfaraz had hit an unbeaten triple century and he is now eyeing another one, a rare feat in any kind of cricket.
In other Group B encounters, Karnataka reduced Railways to 160 for seven at the Karnail Singh Stadium in the national capital.
At the Holkar Stadium in Indore, hosts Madhya Pradesh took a crucial first-innings lead after bundling out Uttar Pradesh for 216 and were placed at 105 for three in their second essay, with skipper Naman Ojha unbeaten on 20 in the company of Yash Dubey (4).
Overall, MP led by 119 runs.
At the Motibaug ground in Vadodara, Saurashtra, who are in a spot of bother at 23 for two, need another 177 runs for an outright win against hosts Baroda.
In Dharamshala: Mumbai: 372/5 v/s Himachal Pradesh – No play on Day 2.
In New Delhi (Karnail Singh Stadium): Railways 160/7 (Avinash Yadav 62, Arindam Ghosh 50 not out; Prateek Jain 4-29, Abhimanyu Mithun 2-38) v/s Karnataka.
At Indore: Madhya Pradesh 230 and 105/3 (Rameez Khan 32, Rajat Patidar 25; Saurabh Kumar 2-15) v/s Uttar Pradesh 216 (Saurabh Kumar 98 not out; Rinku Singh 53; Ravi Yadav 5-61; Gourav Yadav 3-73). Madhya Pradesh lead by 119 runs.
At Vadodara: Baroda 154 and 187 (Deepak Hooda 52, Yusuf Pathan 46; Jaydev Unadkat 6-72, Chetan Sakariya 2-39) v/s Saurashtra 142 (Harvik Desai 31, Chirag Jani 29; L Meriwala 5-64; A Sheth 3-25) and 23/2 (Avi Barot 12; L Meriwala 2-17). Saurashtra need 177 runs to win.