Middlesex 187 (Buck 4-51) and 374 for 9 (Holden 94, Harris 79*, Robson 72) lead Northamptonshire 346 (Vasconcelos 140, Harris 7-83) by 215 runs
Max Holden and James Harris gave Middlesex hope of producing a remarkable turnaround against Northamptonshire at Wantage Road. The pair added 121 for the seventh wicket on the third afternoon to help steer Middlesex to 374 for 9 following-on, leading by 215.
At 166 for 6 just after lunch, and a lead of just seven, Middlesex were slumping to defeat. But Holden and Harris gathered themselves and began to work their side back into the game with careful, considered batting with the clouds parting and the zip from the surface easing.
Holden led the resistance, simply happy to occupy the crease. He left the very ball well and nudged and flicked his way to an 83-ball fifty - his second of the summer - but it did include a sumptuous cover-drive, one of eight boundaries.
Harris was a more jittery early on and cut and missed several times and edged Brett Hutton just short of first slip. But he too was prepared to ground it out and take the innings as deep as possible.
Holden, on the ground where he spent a profitable loan spell last season, got to within six of a maiden Middlesex century against the second new ball but, agonisingly, drove loosely at Hutton and edged to second slip. He peeled himself from the field having undone all his hard work with a shot he had largely ignored for his previous 163 balls.
After Holden fell, the lead was only 128 and Northants had ambitions to run through the lower order. But Harris wasn't finished and went past his own half-century - a third in this year's Championship - in 138 balls with seven fours.
Harris managed to take Middlesex to the close, 79 not out, sharing a stand of 54 with 19-year-old Ethan Bamber on debut, and No. 11 Tim Murtagh then holding out to stumps.
Such a recovery was beyond the ambitions of the most ardent Middlesex supporter as they slumped just after lunch with Northants again excellent with the ball. They took three wickets in three overs after an initially quiet 45 minutes play. Nathan Buck nipped a ball into Stevie Eskinazi to win an lbw decision before Rory Kleinveldt swung a ball into Dawid Malan to remove his off bail for just 5 and another to Eoin Morgan that trapped him lbw for a third-ball duck.
Sam Robson battled away well for 11 cloudy overs on the second evening and went on to make 72 - his highest score of the season - before gloving a catch down the leg-side in the final over before lunch and when Robbie White was caught at slip for 5 after the break, the game was only heading one way.
But Holden and Harris ensured Middlesex have a fighting chance of pulling off just a fifth first-class win when following-on. They were helped by the 56 extras Northants conceded - the most Northants have given Middlesex in a first-class innings - taking the match tally given by Northants to 93.