The teenage leg-spinner took two wickets as Ben Stokes' side bowled out their hosts on the opening day of the third Test; England then lost Zak Crawley before stumps
Karachi (day one of five): Pakistan 304, England 7-1 - England trail by 297 runs with nine first-innings wickets remaining
Rehan Ahmed took two wickets on his first day as England's youngest men's Test cricketer – and Jack Leach picked up four – as the tourists enjoyed another positive day in Pakistan.
Rehan, 18, had only played three first-class matches before Ben Stokes and Brendon McCullum handed the Leicestershire allrounder his debut, and the youngster repaid that faith with an accomplished spell through the second and third sessions of the first day in Karachi, picking up the scalps of Saud Shakeel and Faheem Ashraf as his reward.
Pakistan had won their first toss of the series and made four changes to the side beaten at Multan, which gave England an unassailable lead ahead of the final match in a historic tour. But Babar Azam's charges were guilty of profligacy on a blameless pitch, finding ways of needlessly throwing away starts.
They did earn a late fillip, though, with Zak Crawley trapped in front by Abrar Ahmed in the short period before stumps.
Rehan Ahmed embraced his father, Naeem, after being presented with his cap (Matthew Lewis/Getty Images)
Babar was run out for 78 via Harry Brook and a terrific take from Ben Foakes, recalled by England for the first time in this series, as the home captain attempted a sharp single to square leg.
By then, however, he had already watched as Abdullah Shafique (8) was trapped in front by Leach, who was the first England spinner to share the new ball in the first innings of a Test since Jack White in 1921.
Shan Masood (30), a replacement for the injured Imam-ul-Haq, top-edged a hook to fall straight into a telegraphed trap, before Azhar Ali (45) – in his final Test before international retirement – did exactly the same, gloving through to Foakes to give Robinson, battling a dodgy stomach, a wicket just before lunch.
At that point, Rehan had bowled five overs at a cost of 37 runs. But he settled into his work terrifically thereafter; he beat Shakeel (23) with a googly that fizzed through the air and ragged past his outside edge.
That delivery appeared to settle the youngster, whose next ball landed in the same spot but was a traditional leg-break, taking the left-hander's inside edge and looping up for Ollie Pope to take an excellent short-leg catch diving forward.
Babar Azam was run out for 78 (Asif Hassan/AFP via Getty Images)
Seven overs later, England had a fifth wicket, Mohammad Rizwan (19) plinking perhaps the worst ball of the day – a knee-high full toss from Joe Root – straight to Stokes at mid-on, with neither bowler nor fielder able to contain their laughter.
Once Babar was run out, Salman Agha (56) took on responsibility as the senior batter, particularly once Rehan trapped Ashraf with a fine googly that pitched on middle and straightened to hit his back pad. Nauman Ali played aggressively for 20, but the spinner – in for Zahid Mahmood – fell to Leach, his opposite number, as he lined up a slog-sweep.
Leach claimed his third when Agha ran past a ball that turned prodigiously as he attempted to make headway alongside the tail, and he picked up his fourth two balls later, bowling Abrar with a beauty.
With three overs to negotiate before the close, Crawley was trapped in front by Abrar without scoring to give Pakistan a late breakthrough.