England in their second innings were 121 without loss at lunch here on Monday, a lead of 98, after Trescothick had been missed by Akmal on six and seven while his side were still behind. England captain Andrew Strauss was also 54 not out.
The hosts resumed on three without loss, a deficit of 20, with Trescothick, whose previous best score this series was his first innings 28, unbeaten on nought and fellow left-hander Strauss three not out.
Three overs into the day's play Trescothick flicked at Mohammad Sami but Akmal was slow to react to the gloved legside chance and only got one hand to the ball, England then 17 without loss.
Next over Akmal spilled an even easier chance when Umar Gul produced a superb lifting delivery which took the outside edge of Trescothick's bat.
But despite getting two hands to the ball Akmal, somehow dropped the straightforward catch, with England's score having moved on to 22.
England had provoked plenty of discussion by dropping keeper Geraint Jones and bringing in Chris Read, long regarded as the better gloveman, but all eyes were now on Akmal.
His misses, on a pitch where the ball was starting to keep low, threatened to have a major impact on a game Pakistan, 1-0 down in the four-match campaign, had to win to keep alive hopes of clinching the series come the final Test at The Oval later this month.
However, there were no consoling words from his captain as Inzamam-ul-Haq was off the field for the first hour with a rib injury sustained after he fell over his stumps Sunday while getting out hit wicket to Monty Panesar.
Trescothick, on 21, edged Gul just wide of second slip before he found his touch by straight-driving the paceman for four.
Runs were now coming briskly, 65 scored off the day's first 10 overs.
Strauss was more assured, square-cutting Sami for four.
But, on 29, he appeared very fortunate to survive an lbw appeal from leg-spinner Danish Kaneria with West Indian umpire Billy Doctrove unmoved.
Kaneria suffered further when Trescothick, using his feet, went down the pitch to loft him for a six that saw England to a century opening stand.
Strauss completed a 68-ball fifty with six boundaries when he pushed seamer Shahid Nazir into the offside before Trescothick reached the landmark in 88 balls when he swept Kaneria for his eighth four.
Trescothick's luck held when on 53 he played defensively at a Nazir delivery and the ball just bounced over his stumps.
Pakistan, who made 538 in reply to their opponents' 515, were 23 runs ahead on first innings after a third-wicket stand of 363 between Younis Khan (173) and Mohammad Yousuf (192), their best Test partnership against England.