The 23-year-old might cut an unusual figure at the crease as he bats in spectacles, but he only had eyes for a ball that he regularly sent to the Bristol boundary.
Imam took advantage of a true pitch, small boundaries and a lightning-fast outfield to make 151 from 131 balls – the highest ODI score by a Pakistan player against England and fifth-best in the country's history. He struck 16 fours and a six.
— PA Sport (@pasport) May 14, 2019
Chris Woakes was the pick of the England bowlers as he finished with figures of 10-0-67-4, his 11th four-wicket ODI haul.
On a day of landmarks, captain Eoin Morgan broke Paul Collingwood's England record of ODI appearances by playing 198th game.
England rested Jos Buttler after his batting pyrotechnics in Southampton on Saturday.
Buttler was stood down after his match-winning unbeaten 110 from 55 balls – England's second-fastest ODI hundred – and Adil Rashid also dropped out as Joe Denly and Tom Curran came in.
That allowed Jonny Bairstow the chance to keep wicket in a ODI game for the first time in nearly three years.
But Bairstow's work was not without error as he spilled Haris Sohail on 24 after Liam Plunkett had been gloved low down the legside.
Imam held the Pakistan innings together after England, perhaps wishing to get some experience of chasing with the World Cup in mind, had won the toss and decided to bowl.
Woakes found some early movement to dismiss Fakhar Zaman and Babar Azam and leave Pakistan 27 for two in the fifth over.
Fakhar had made 138 at Southampton but he lasted only four balls this time as Joe Root accepted his slip catch at the second attempt.
Babar showed signs of menace in his 15, but Woakes breached his defence with a beauty that nipped back off the seam and took the top of off-stump.
Pakistan recovered with two 50 partnerships, although Haris' run-a-ball 41 could have been so much more.
Haris was punished for some awful running between the wickets, the nifty footwork of Curran leaving him stranded when a little bit of urgency or a final dive would have save him.
Sarfaraz Ahmed had made 27 from 34 balls when he hoisted Plunkett high into the air at fine leg and substitute fielder Chris Jordan claimed the steepler.
Imam and Asif Ali – who made an ODI best of 52 – went on the attack in their fifth-wicket partnership of 125 as England's bowling became slightly ragged.
Asif hit three sixes and two fours in his 43-ball stay before he struck Woakes to Jason Roy at mid-off.
Imam, the nephew of former Pakistan batsman and current chief selector Inzamam-ul-Haq, had completed his sixth century from 27 ODIs before Curran finally ended his resistance by bowling him.
Those dismissals briefly stunted Pakistan's late push for runs as Curran claimed a second wicket and David Willey a first.
But Hasan Ali smashed an unbeaten 18 from nine balls to steer Pakistan to 358 for nine, and ensure England would have to overhaul an imposing total.