Northamptonshire face an uphill struggle after they slumped to 89 for three after Dawid Malan's unbeaten 154 propelled Middlesex to 488 for nine declared.
Malan, on 72 overnight, batted patiently for almost six and a half hours and faced 258 balls. He was content to be the support act in an important sixth-wicket stand of 128 with John Simpson, who played fluently for his 67.
Tim Murtagh then put bottom-of-the-table Northants up against it almost immediately with the last ball of his second over to have James Middlebrook caught behind for a duck.
Toby Roland-Jones, replacing Steven Finn at the Pavilion End, saw Stephen Peters thick-edge to second slip on 18, while Finn enjoyed his first success with his second ball back when he was switched to the Nursery End as Matt Spriegel chopped a short ball into his stumps.
James Kettleborough, a 21-year-old playing only his second first-class match, batted well to reach 42 not out and keep Northants afloat in the 26 overs possible before rain arrived to lop the last 16 overs from the day.
— Michael Hall (@mihall44) June 30, 2014
Rob Newton is with him on 18 not out, but Middlesex will fancy their chances of pushing for a fifth victory of the season.
Resuming on 280 for three, Middlesex lost Neil Dexter for 20 to the eighth ball of the day, lbw to Muhammad Azhar Ullah who, with Steven Crook, bowled well with a second new ball that was immediately available.
Joe Denly survived a big appeal for a catch at the wicket off Azhar on 14 before, on 17, driving Crook to mid-off, where Maurice Chambers dived forward to scoop up a good catch.
At 308 for five, Middlesex were in danger of wasting the hard work of their top three, but Malan and Simpson responded with a determined stand.
Malan, in particular, resisted the temptation to go after anything slightly wide and, as a result, scored only 24 runs in the morning session as Middlesex reached 364 for five at lunch.
Malan might have been caught on 96 from the last ball before the interval when he hit Crook straight at short-leg, but was saved by a kind rebound. He reached his first championship hundred since 2012 soon after lunch.
— Middlesex Cricket (@Middlesex_CCC) June 30, 2014
Andrew Hall offered him a juicy leg-stump half-volley and he gratefully stroked it to the midwicket ropes for his 16th four.
In all, Malan hit a six and 19 fours while there were nine fours and a six from Simpson’s bat before he perished attempting to pull Spriegel’s off-spin and being trapped lbw.
Roland-Jones and Finn contributed a few tail-end blows before being caught in the deep, swinging Spriegel and Middlebrook, respectively, to leg and Murtagh aimed a violent blow at his very first ball, from Spriegel, only to be bowled.
Malan, by then, had gone past his previous championship-best, 143 against Derbyshire at Lord’s in 2011, but when the declaration came he was still two runs short of his first-class career-best, an innings of 156 not out against Cambridge MCCU last year.
Malan said: "I needed that hundred - it's been a long time since my last one, and I definitely had a bit of the nervous nineties today.
"It was also a nervous 40 minutes at lunch on 96 not out. They tried to frustrate me out a bit by bowling wide of my off stump, but I was pleased to get there in the end and it was important for us to put a big total on the board."
David Ripley, the Northants head coach, is remaining positive about his side's prospects.
"Losing those 16 overs at the end of the day helped us. It's still a good pitch and we have a chance to bat well tomorrow and to take time out of the game," he said.
"Getting past the follow-on target is our first priority, of course. James Kettleborough batted very well to get to 42 not out, and he has earned his chance in the championship team by scoring a lot of runs for the second XI. He's been chomping at the bit to play, and he has coped well out there so far."