With Beaumont and Knight at the crease, the pitch looked flat, the batting looked easy and England was on course for a big total.
However, for the second game in succession, a middle-order collapse threatened to derail the tourists' innings.
Jess Kerr removed Knight and Sciver-Brunt with two well-executed slower deliveries before Alice Capsey was stumped by Fran Jonas.
Beaumont had remained calm at the other end, picking her moments to attack as she moved towards a 10th ODI century.
A rush of blood denied her that milestone as she walked at Hannah Rowe and drove the ball to mid-on with an ugly leg-side drive.
It was a shot completely out of sync with the controlled aggression Beaumont had shown up to that point, and when Danni Wyatt and Charlie Dean fell soon after, England was in trouble at 166-7.
After her match-winning knock in Wellington, it was left to Jones to rescue them again with another valuable counter-attacking innings.
The wicketkeeper-batsman was well supported by Kate Cross to get the visitors to a useful total, but as impressive as Jones has been, England would prefer their number seven not to be needed as often as she has been in this series.