Worcestershire claimed two wickets during the morning session as they searched for victory in the LV = County Championship clash with Leicestershire at New Road.
Charlie Morris and Saeed Ajmal picked up one apiece but the visitors batsmen showed plenty of defiance and determination in the two hours before lunch.
Leicestershire, who had been set a 458 target, resumed on 56-2 with Greg Smith unbeaten on 38 and Dan Redfern one.
Morris and Ajmal, on the last day of his current spell at New Road, opened the attack.
It was Morris who made the first breakthrough of the morning with his 33rd Championship wicket of the campaign.
Smith on 46 pulled a short ball from Morris straight into the hands of Tom Fell on the mid-wicket boundary with the total on 75.
Redfern clipped Ajmal for two off his legs to bring up the 100th in the 38th over.
Leach came on for Morris whose figures at that stage were 13-7-22-2.
Cobb was fortunate when he edged Leach wide of Mitchell at slip when on 17 out of 105-3. AJmal claimed his first wicket when Redfern (29) prodded forward and Tom Kohler-Cadmore held onto the chance at second slip.
Leicestershire were then 113-4 in the 39th over.
Cobb and new batsman Niall O'Brien showed plenty of fight as the Worcestershire bowlers probed for more success.
Morris switched ends to replace Ajmal at 149-4.
Leicestershire reached 165-4 off 52 overs by lunch with Cobb on 30 not out and O'Brien unbeaten on 37.