After Worcestershire declared their first essay on a huge 650 for seven wickets, Zaheer's devastating bowling had Essex running for covers and they were 186 for nine at stumps on day two.
Essex opener of Indian origin Varun Chopra (53) and Mark Pettini (48) shared 117 for Essex but Zaheer soon hit back with vengeance.
Zaheer will be eyeing last man Darren Gough's wicket to complete his collection when play resumes today.
His bowling figures, so far, read 21.3-6-65-9.
''There was some reverse swing and it was one of those days when everything I did came off. I just kept putting the ball in the right areas and if you do that, it puts pressure on the batsmen.
''There were some excellent catches by first slip and the wicketkeeper but I don't think the wicket was doing a great deal. I did start to think about taking all 10 wickets once the eighth wicket fell and it would be marvellous to achieve that - but the main thing is that Worcestershire are in a strong position,'' Zaheer said.
''It would be nice though to get that final wicket in the morning,'' added the Team India discard.