England 92 for 4 (Pope 46*, Buttler 15*) trail Pakistan 326 (Masood 156, Azam 69) by 234 runs
A career-best innings from Shan Masood answered every question England had asked of Pakistan on the first two days of this opening Test.
Masood batted for nearly eight hours and faced 319 deliveries for his 156, which highlighted an ability to adapt throughout the course of an innings and effectively told the story of his cricketing life so far.
Not long into the evening session, it was Pakistan asking all the questions when Shaheen Shah Afridi trapped Rory Burns lbw with the fourth ball of England's innings and Mohammad Abbas accounted for Dom Sibley and Ben Stokes to put the hosts under pressure at 12 for 3.
By the close, Ollie Pope had played a steadying hand with an unbeaten 46, but it was going to take much more from him and Jos Buttler, who was not out 15, come the third day after Joe Root was dismissed by Yasir Shah for a battling 14.
Masood resumed on 46 having played a supporting role to Babar Azam the previous day. As opener, Masood had navigated a tricky start in which Stuart Broad and James Anderson bowled tight opening spells.
But England's bowling attack had lost all potency post-lunch on the first day and Masood and Azam cashed in where possible without taking too many unnecessary risks, save for Masood's ill-advised charge at Dom Bess which ended in a missed stumping by Buttler. Masood had earlier survived a dropped catch by the wicketkeeper off the same bowler.
When Azam failed to add to his overnight score of 69 in the face of some improved England bowling on the second morning, Masood took the lead role, although he could have been upstaged had Shadab Khan not got too flashy and skied Bess straight to Root at mid-on after a knock of 45 from 76 balls that was, until that moment, very sharp.
Most impressive from Masood has been his ability to show how far he has come after past disappointments against England - and particularly Anderson - learning from experience and changing for the better.
Masood left balls on the fourth-stump line that he would prevoiusly have nicked off to and played with soft hands when he had to so as to avoid offering chances to the slips.
So when Anderson struck with his sixth ball of the day, luring Azam into an attempted drive that ended up in the hands of Root at first slip, Masood didn't panic.
When Anderson and Broad bowled six maidens on the trot between them, Masood maintained the patient approach that had got him this far. Indeed, it was Asad Shafiq who scored Pakistan's solitary run from eight overs bowled by Broad and Anderson in that period.
Shafiq fell for to Broad for 7, caught by Stokes at second slip, followed by Mohammad Rizwan, caught behind off Chris Woakes, to leave Pakistan 176 for 5. That brought Shadab to the crease and, having negotiated their way to lunch, Masood adapted after the break. The pair fell into a lovely rhythm of shot-making and nabbing quick singles that frustrated England's bowlers throughout a sixth-wicket partnership worth 105.
England had only conceded 48 runs during the morning session but saw Pakistan regain the momentum immediately after lunch, as Bess and Root bowled ahead of the arrival of the second new ball. Masood then stroked his way through the 90s in half-a-dozen balls to bring up his hundred, loudly celebrated on the Pakistan balcony.
The partnership should have been more but Shadab's wild swing at Bess ended things, although it sparked another change in gears from Masood. What looked like being a rebuilding job, became something else when Jofra Archer dismissed Yasir and Abbas with consecutive balls, the former without adding to his score of 5 when he was dropped by Buttler off the bowling of Bess.
Masood flicked the switch, seeking as many runs as he could get before he ran out of partners. He took 16 off one Bess over, including two sixes in three balls, was keen to run a second to bring up his 150 and did when Buttler's relay shy at the stumps went wide and he wore a Broad short ball painfully on the elbow, all before tea.
Masood didn't last long after the break, falling lbw to a Broad delivery that nipped back and struck the back pad on line with leg stump. But by then he had more than done his job, racking up his third consecutive Test century after tons against Sri Lanka in December and Bangladesh in February, the fourth of his career overall.
Pakistan's bowlers kept up the good work with Abbas particularly damaging in picking up the wickets of Sibley and Stokes for nought in the space of eight balls. The delivery that bowled Stokes was an absolute diamond that found just enough late movement to beat the bat and kiss the top of off stump.
Naseem Shah showed his pace with no reward and when Yasir chimed in with a faint edge off Root which went through to the keeper, England were left looking to Pope and Buttler to erase a deficit still north of 250.