The second ball of Imad Wasim's third over gave it away.
Imad has admitted in the past that he hardly tries to spin the ball in this format but by the second half of England's innings it had become clear that with the Headingley pitch baking in 30-degree heat, the pitch was offering something. Imad tossed the ball up, slower than usual, outside Liam Livingstone's off stump and it gripped in the surface as he punched to cover. If England's decision to pick two frontline legspinners for the first time in T20 internationals hadn't already made it clear that this was a day for spin, Imad - Imad! - turning one sharply on a length confirmed it.
Pakistan's two spinners, Imad and Shadab Khan, ended up returning 3 for 70 between them in a combined eight overs, and England's response was immediate at the start of the chase. Adil Rashid was thrown the new ball, reprising the role he filled so successfully in India four months ago, but it was in the middle overs that England's spin-heavy strategy became apparent.
Every ball between the end of the Powerplay and the start of the 17th over was bowled by a spinner - either Rashid, Matt Parkinson or Moeen Ali - and in those 60 balls, England won the game, conceding 81 runs and taking five wickets to rip through Pakistan's middle order. Never before had they bowled so many overs of spin in a single T20I - even though Livingstone, whose bowling has helped springboard him into contention for a starting spot in the World Cup, went unused.
The strategy stood in contrast to that used by England in India earlier this year, when Eoin Morgan's assessment of the Ahmedabad pitches was that fingerspin would be completely ineffective against a strong home batting line-up. Instead, this game served as ideal preparation in the event that the pitches served up in the UAE for October's World Cup - which will have been used for the remainder of the IPL immediately before - turn out to be dustbowls.
The biggest beneficiary of their strategy was Parkinson, who only a month ago was seen as England's fifth-choice spinner behind Rashid, Moeen, Livingstone, and Liam Dawson (who is not involved in this series following his self-isolation). Parkinson's method stands in stark contrast to Rashid's, tossing the ball up above batters' eyeline and almost exclusively bowling legbreaks with the occasional slider thrown in for good measure, but after his confidence was dented by a tough 10-game stretch in the T20 Blast this year, his stock has risen sharply in the past two weeks since his last-minute ODI call-up.
He had started brightly at Trent Bridge on Friday night, conceding only 11 runs from his first two overs without conceding a boundary, but was targeted by Babar Azam and Mohammad Rizwan in his final two, who hit him for three sixes towards the short boundary at midwicket even as he hung the ball wide outside off. Four overs for 47 was not far below par on a night where 433 runs were scored in 39.2 overs, but it was a chastening end nonetheless.
In Leeds, he recognised that conditions were in his favour and stuck to his strengths. ESPNcricinfo's ball-by-ball data recorded 24 legbreaks and no variations in his four-over spell, and his speeds ranged from 44-50mph (71kph-80kph). He conceded a single boundary, when Imad Wasim launched him over his head for six, and roared in celebration with both fists clenched when Azam Khan walked past the final ball of his spell to leave him with 1 for 25.
The contrast between Parkinson and Rashid was particularly apparent when they were bowling in tandem, and hinted that it might not be impossible for them to play in the same side more often - even if it means sacrificing some of the batting depth which has been so key to their approach. Rashid's wealth of variations means he is more comfortable bowling to left-handers or when defending a short boundary, and on a turning pitch, Parkinson is a much more attacking option than Dawson, albeit without his batting or his ability to bowl in the Powerplay.
Equally significant for England was Moeen's success, with bat as well as ball. His 16-ball 36 was a vibrant, modern T20 innings, taking down his match-up by carting a four and a six in the three balls he faced from Shadab, and cracking Haris Rauf away through the ring to make the most of the final Powerplay over. With the ball, he conceded 32 from his three overs, but his sharply-spun offbreak to Fakhar Zaman which beat his outside edge and slid into the top of off stump was the perfect fingerspinner's dismissal. Pakistan's approach - in particular, their decision to send Mohammad Hafeez in ahead of Zaman and Azam Khan - might be called into question, but England's execution was near-perfect.
"The two legspinners in particular bowled fantastically well: Parky and Rash complemented each other brilliantly," Moeen said. "They're very different, but both very skilful. If conditions come the World Cup do spin, we're going to have to bowl well.
"I've not bowled for England for a while but today was great conditions for a spinner. It's not always going to be a high-scoring game - when it's spinning and it's quite a small ground, you're skill going to see high scores. Sometimes it's not like that when it's a complete dustbowl but it was a great toss to lose."
The result is that England seem better-placed than many would think if they end up playing on a slow, used pitch in the T20 World Cup, not least after Friday's draw saw them avoid any Asian sides in the group stage (barring qualifiers from the first phase). Their batters have both the attacking intent and the skill to take down spin, and their spinners have the quality to exploit conditions to their advantage; as a dry run for a dry pitch, this could hardly have gone better.

Matt Roller is an assistant editor at ESPNcricinfo. @mroller98