UP tried to bat out the opponents and were 361 for seven at stumps in their second essay with skipper Suresh Raina and Ravikant Shukla also scoring half centuries.
Jyoti Yadav was occupying the crease at 47 with Amir Khan (0) yet to face a delivery.
Resuming from an overnight score of 14 without loss, UP began the day on a sedate note with caution being the word for both the openers.
Shiv Shukla (36) was first to go when he edged behind a Tahir Mughal delivery to Khalid Mahmood after adding 57 runs for the first wicket with Rohit Shrivastava.
Shrivastava (31) was next to go when he gloved a short-pitched ball from Sehzad Malika and Mahmood made no mistake. UP were 95 for two at the stage.
Captain Suresh Raina was in good nick and scored at brisk pace.
With Pakistan pace ace Mohd Asif nursing shoulder injury, Raina looked to cut loose and reached his 15th first-class half-century.
He was particularly severe on Abdur Rehman and hit him for consecutive fours before the left-arm spinner castled him for 55.
Raina added 70 runs for the third wicket with Ravikant Shukla.
Shukla batted in contrasting style without taking any chances.
Shukla added 73 runs with Rizwan Shamshadns and took the total to 238 before edging a Tahir Mughal delivery to the slip. Shukla took 125 balls for his 64.
All this while a calm and composed Shamshad guarded against taking chances and it was only after Shukla departed, Shamshad stepped on the gas and chanced his willow on one and all. Be that left-arm seamer Sarfaraz or Tahir Mughal, they were all cut, pulled and driven in same vain without discrimination.
Shamshad finally fell, again in 80s, when he top-edged a short-pitched ball from Manzoor Ahmed to be taken safely by Atiq-ur-Rehman.
Shamshad's 88 came in 131 balls and were studded with eight fours and one mighty hit over the ropes.
Shamshad and Jyoti together added 88 runs for the fifth wicket.
The next two wickets fell in quick succession as P Kumar (1) and Piyush Chawla (8) were removed by Tahir and Majid Jahangir respectively.
Tahir was most most successful, if not economical, of the Sialkot bowlers and ended up with the figures of 96 for three in 22 overs.
Brief scores: UP 316 and 361 for 7 (R Srivastava 33, Shiv Shukla 36, S Raina 55, R Shukla 64, Rizwan Samshad 88, Jyoti Yadav 47 not out; Tahir Mughal 3 for 96, Majid Jahangir 2 for 28) vs Sialkot 261.