Cook, with only 106 runs in eight Test innings this season, was the man under immediate pressure when play began.
He opted to replace introspection with bravado, riding his luck with some streaky shots through the slips before settling down to play a series of cracking pulls and cuts off a wayward attack.
Cook was gifted his 13th Test century in unusual circumstances when Mohammad Asif gathered the ball from a routine forward defensive short and hurtled it over a startled wicketkeeper Kamran Akmal to the boundary for four overthrows.
"I've been feeling under pressure which is natural when you are not scoring any runs," Cook told a news conference. "I tried to be more positive and I just went out there today trying to hit the ball and trying to score runs."
Only two wickets fell in the opening two sessions before left-arm pace bowler Mohammad Amir and off-spinner Saeed Ajmal took three wickets apiece from 15.2 overs.
The rot began when Kevin Pietersen was bowled for 23 through the gap by Ajmal in the first over after tea. Ajmal also bowled Eoin Morgan (5) and Graeme Swann (6).
"Obviously it got quite dark under the floodlights and they bowled really well," Cook told a news conference. "They were reversing the ball and it spun."
In the knowledge that Pakistan, the most volatile team in world cricket, can blow and hot and cold several times in the same match, Cook said he believed England could still clinch the series on Saturday.
"Without a doubt," he said. "Hopefully we can eke out some more runs. You know when Pakistan are on top they are a very good side but if we can apply some pressure and take early wickets then suddenly 150 more runs, 160 runs looks a really long way."
Salman Butt, the Pakistan captain, said his team would take heart from their upset win over Australia in the second test before the England series began.
"It [victory] should be something can achieve," he said. "The batsmen who have played their strokes and played aggressively have got runs.
"For one session it looked England had made a great comeback in the game then there was one good session for the bowling side. It's the nature of this game, wickets have been falling in clusters."