Assuming Northamptonshire's survival qualities do not improve substantially, Middlesex will expect to regain top place in the First Division of the County Championship with a fourth win in six matches.
They have the struggling promoted side four wickets down and still 172 runs behind after their ruthless punishment of Northamptonshire's bowling earlier in the day set up a lead of 260.
There were career-best innings for Neil Dexter and Toby Roland-Jones, in the latter's case a second of the match after his medium pace claimed six wickets for 55 on Monday. The four sixes struck by Roland-Jones in his 30-ball 60 doubled his career tally, having hit four in 43 first-class matches before today.
Dexter and Joe Denly had dominated the morning session, turning an overnight deficit of 21 runs into a lead of 99 by adding 120 runs in the first session without giving a chance. Dexter completed a 195-ball hundred with the last ball before lunch, after which Denly fell to the second ball of the afternoon, caught at slip off Andrew Hall for 70 – his previous highest this season having been eight.
But it was when Roland-Jones swung the bat that Northamptonshire began to suffer seriously. He despatched James Middlebrook over the boundary rope off consecutive balls and treated Maurice Chambers and Hall with similar disdain as the pair added 94 in 47 balls.
Their assault ended with the Middlesex seamer holing out to long-on, prompting a declaration. Dexter finished on 163 not out while Chambers ended up with 0 for 107, which may be a career-worst, or somewhere very close.
Northamptonshire were left with 36 overs to survive simply to take the match into a fourth day and their cause did not begin well when Middlebrook was bowled first ball off an inside edge facing Tim Murtagh.
Roland-Jones continued to put his signature on the match with his seventh and eighth wickets, but Matt Spriegel and Rob Newton got their heads down for an hour and a half to ensure that a three-day defeat was avoided. Spriegel fell to the last ball of the day bowled by Denly, an inside edge that bounced off his boot to Ollie Rayner at first slip.
Sky Sports Sixes League
Derbyshire's Marcus North has taken an early lead in the Sky Sports Sixes League as he cleared the boundary six times in his innings of 90 against Leicestershire at Grace Road in the NatWest T20 Blast. Nestled in just behind him is Jason Roy, the competition's leading run-scorer who has passed fifty in both his innings so far. England and Middlesex's Eoin Morgan impressed in front of the cameras this week with 77 from just 43 deliveries against Essex at Lord's.
Marcus North (Derby) 6/47
Jason Roy (Surrey) 6/90
Eoin Morgan (Middx) 4/72
Jordan Clark (Lancs) 3/20
Ravi Bopara (Essex) 3/24
Josh Cobb (Leics) 3/28
David Willey (Northants) 3/28
Matt Coles (Hants) 3/29
Michael Lumb (Notts) 3/29
Scott Styris (Leics) 3/31