Northamptonshire 126 for 4 (McManus 39) trail Middlesex 625 for 8 dec (Holden 151, Williamson 114, du Plooy 105*, Cracknell 73, Robson 57) by 499 runs
Kane Williamson and Leus Du Plooy scored centuries as records wanted and unwanted were set on day two of Middlesex's Rothesay County Championship clash with Northamptonshire at Merchant Taylors' School.
Former New Zealand Test skipper Williamson's 114 came on his Championship debut for the Seaxes, while Du Plooy's unbeaten 105 was his first in four-day cricket this season.
Williamson and Max Holden (151) took their mammoth second wicket stand to 239, so eclipsing the 222 of Sydney Brown and Bill Edrich at Lord's in 1949 and, with Joe Cracknell adding a blistering 73 Middlesex totalled 625 for 8, their highest ever score against the Steelbacks.
Saif Zaib took 3 for 70 amid the run-fest, but fellow spinner Yuzvendra Chahal returned 0 for 175 - the worst return by a Northamptonshire bowler without taking a wicket in Championship history - all on his 35th birthday.
Needing 476 to avoid the follow-on, Northamptonshire reached 54 without loss before stumbling to 126 for 4 by the close, Lewis McManus top scoring with 39, Ryan Higgins taking 2 for 17.
Williamson moved smoothly from his overnight 88 not out to a century completed with two runs into the leg-side. Day one centurion Holden looked a little scratchy before two boundaries took him past 150. However, no sooner had he reached the landmark when Ben Sanderson trapped him lbw on the back foot.
As so often with huge stands both protagonists fell in quick succession, Williamson pinned in front by Liam Guthrie in the next over.
Despite the double strike, the hosts hardly missed a beat, Higgins and Du Plooy sharing a stand of 67 in only 13 overs. Higgins drove the ball crisply to make 35 before Zaib struck twice in two balls, first removing the all-rounder leg-before and then trimming Ben Geddes' off-bail.
Any Northamptonshire hopes of getting the hosts for under 500 were quashed either side of lunch with Cracknell, who made 100 in the reverse fixture a month ago playing a gem of a knock.
The wicketkeeper/batter, in the wilderness until the recent arrival of Dane Vilas, twice cleared the ropes and cut and swept with authority, playing the dominant hand in a stand of 124 with skipper Du Plooy. He eventually fell hooking one from Dominic Leach to Guthrie at long leg and when Zafar Gohar and Toby Roland-Jones fell cheaply there were fears Du Plooy would run out of partners before reaching three figures.
Du Plooy, who'd earlier thrashed a full-toss from Chahal back over the bowler's head for six, looked unperturbed, driving stylishly and stroking the ball into the gaps. His 10th four brought him to 100 in the shadows of tea.
Tom Helm provided great support with two huge sixes in a sprightly cameo, allowing the hosts to declare at the interval.
Northamptonshire began brightly, McManus unfurling a flurry of boundaries, Middlesex's left-arm seamer Noah Cornwell on the receiving end of the flack.
He and Ricardo Vasconcelos rattled up a 50-stand, but the left-hander played a little skittishly before edging Higgins to Du Plooy at slip, who clung on at the second attempt.
Aadi Sharma was dropped on nought by Holden at long leg to deny Higgins a second wicket, but his response was to trap McManus lbw with his next delivery.
Gohar soon found the edge of James Sales' bat, and though Sharma threatened to make the most of his reprieve with some wristy cuts and fluent drives he too fell to Roland-Jones in the death throes of the day.
