Pakistan were 211 for five at lunch, still 83 runs behind Zimbabwe's first innings total of 294, with Younis unbeaten on 76.
Only 48 runs were scored in 28 overs during the morning's play for the loss of two wickets.
Pakistan captain Misbah-ul-Haq made a laboured 33 off 120 balls before he fell victim to the second delivery with the second new ball, caught at first slip off left-arm bowler Brian Vitori, pushing at a wide ball slanted away from him.
Younis, man of the match after making an unbeaten double century in Pakistan's win in the first Test, played cautiously on a pitch with several cracks which is expected to deteriorate.
He added 24 runs to his overnight 52. He was stuck on 65 for 33 deliveries on either side of the new ball and faced 89 balls during the morning, hitting three boundaries.