England Women 187 for 5 (Beaumont 82, Winfield 74) beat Pakistan Women 119 for 7 (Asmavia Iqbal 35, Hazell 2-18) by 68 runs
Beaumont, who set a new record for runs in a three-match ODI series with her tally of 342 against Pakistan Women, made 82 off 53 balls and Winfield 74 off 45 to lead England to their highest total in the format. It followed their 235-run opening stand in the second ODI at New Road when they both hit centuries.
"There's a lot more freedom," Beaumont said of her form and the team's success. "To go out there and do it, and know that if you fail it is not going to be the end of the world."
There were nine double-figure scoring overs in England's innings, the highest being 19 off the third bowled by Maham Tariq, which kickstarted the charge. Beaumont launched the first six of the innings with a delightful straight drive which crashed into the sightscreen at the Ashley Down End.
Beaumont reached her fifty off 30 balls, and having moved to 82 with nearly five overs remaining had time to score England's first T20I century before falling lbw as she attempted a reverse-sweep, meaning Charlotte Edwards' unbeaten 92, against Australia at Hobart, remained England's best.
As in the one-day series, Beaumont's speed through the ball, power generated with a strong whip of wrists, was a standout feature of her batting.
When Mark Robinson spoke on the day that Heather Knight was appointed captain, he picked out Beaumont and Winfield as players he thought had immense ability to strike the ball but had not been able to translate that to the international stage.
"I needed to work on getting the ball behind me more, in T20 and it was nice that it came off today," Beaumont said. "The coach also said that he wanted me to go out there and strike the ball hard. I have been able to do that too. The other thing is letting it come to me a bit more. A century was in the back of my mind but I will take 82. It would have been nice to have got a hundred, but I'm not worried."
"I have been working really hard on my batting. I had a tough start to my career but it's coming right now and my Dad always said to me 'Remember you start on zero in each innings'. So, I think about that, I think about getting off the mark and then I think about building from there."
Like Beaumont, Winfield struck 10 fours and also a six off Sadia Yousuf and her final score equalled her career-best, having also made 74 against South Africa in 2014. She had a couple of close shaves; there was a tight stumping appeal on 15 when the third umpire adjudged she had a fraction of boot behind the line and then a close run-out chance on 31.
At 146 for 0 in 15 overs, 200 was within reach for England but the last five overs were not quite as fluent as the first 15. The 16-20-over block had fewer runs - 41 - than the other five-over breakdowns.
The final over included a team hat-trick for Pakistan as Nat Sciver edged a swipe, Danni Wyatt was run out and Heather Knight feathered a reverse-sweep to the keeper.
A target of 189 was, unsurprisingly, well out of reach for Pakistan and England's bowling was not stretched in defending the target. Four of the wickets fell to full-tosses, the third of them giving 17-year-old debutant Sophie Ecclestone, a left-arm spinner, her first international wicket when Sidra Ameen picked out deep midwicket.
Asmavia Iqbal struck some powerful blows to finish as top-scorer -- including the one six of the innings, which was Pakistan's first of the tour - before being bowled by Danielle Hazell in the final over.