Tea New Zealand 329 and 326 (Blundell 88, Latham 76, Mitchell 65, Leach 5-66) lead England 360 by 295 runs
Leach, who impressed in the first innings with 5 for 100, duly completed his best match figures of 10 for 166 as he rattled through New Zealand's tail with four wickets in his final five overs. But the instigator of England's surge was once again the indefatigable Potts, whose switch to the Kirkstall Lane End in the first half-hour of the session produced the breakthrough that made subsequent events possible.
It could in fact have been two breakthroughs. With his first ball of the spell, Potts speared an inswinger into Blundell's pads and extracted an lbw decision that was almost identical to the one that had controversially sent the same man on his way in the first innings, at a time when DRS had not been available for a second opinion. This time Blundell was able to send it upstairs, and sure enough the ball was shown to be missing leg. And with Mitchell having similarly survived a review off Leach in the first session, England would have been entitled to believe their luck had finally run out.
Potts, however, was undeterred, and in the very same over, he landed arguably an even bigger fish. No New Zealand batter has ever scored more runs in a series than Mitchell's final tally of 538 at 107.60, but on 56, he walked too far across his stumps to another pinpoint inswinger, and once again umpire Richard Kettleborough raised the finger. This one was shown b Hawk-Eye to be crashing into leg. It also brought to an end an astonishing haul of 724 runs in six partnerships between Mitchell and Blundell, with this latest effort of 113 being their fourth century stand of the series.
By lunch, the pair had added 94 of those runs - 86 of them in a largely fluster-free first session. It was another typically nuggetty display from two men whose frill-free accumulation has been New Zealand's most-consistent antidote to England's hard-pressing new approach.
But despite another tight spell from Stuart Broad and Potts, their outstanding seamer throughout, Mitchell and Blundell set themselves once more for the long haul. Another replacement ball - the 12th of the match - came and went without fuss, and by lunch England were staring at the prospect of their first 300-plus chase of the series.
But all it took was that one breakthrough, and when it came at 274 for 6 - a lead of 243 - England sensed they had their opening. Michael Bracewell, aka "The Beast", emerged with a clear intent to fight England's fiery attitude with some punches of his own, but after launching Leach for one big six over long-on, he was undone two balls later by some more canny captaincy from Ben Stokes, who tempted him to take on the leg-side boundary once again with men set in from the fence at mid-on and deep midwicket. Sure enough, he picked out the latter, Zak Crawley, with a scuff across the line to depart for 9.
The rest came fairly meekly, though not without Blundell at the other end raising his own intensity to build New Zealand's lead with a series of smeared boundaries - including four in his last eight balls - to rush towards his second century of the series. But Tim Southee prodded limply at Leach to be bowled for 2 before Neil Wagner was caught behind for a duck - a thin snick off Leach somehow wedging between Billings' thighs as the keeper stooped to conquer.
There was just time for Trent Boult to smack one more boundary through midwicket before he too was bowled by Leach to complete his second five-for of the match, and the first ten-for of his Test career. Three years after his starring role in the 2019 Ashes Test at Headingley, Leach has reaffirmed his honorary Yorkshireman status in no uncertain terms.
Andrew Miller is UK editor of ESPNcricinfo. @miller_cricket