Middlesex 187 (Buck 4-51) and 32 for 1 trail Northamptonshire 346 (Vasconcelos 140, Harris 7-83) by 127 runs
A fine bowling display from Northamptonshire's seamers forced Middlesex to follow-on at Wantage Road on the second day. After being bowled out for 187, Middlesex then closed 32 for 1, trailing by 127.
Under thick cloud and on a seaming surface, batting was very tricky and having ground out 346 half-an-hour into the morning, the Northants attack then bowled far better than Middlesex managed to take control of the game.
All four Northants seamers contributed with Rory Kleinveldt setting them up with three wickets in seven balls before lunch.
Introduced for the 15th over of the Middlesex reply, he immediately got a ball to climb on Sam Robson to take an edge behind. Next ball, a full inswinger trapped Dawid Malan lbw. Eoin Morgan survived the hat-trick but Kleinveldt produced a third wicket with a full delivery that Stevie Eskinazi drove lazily at to edge to first slip.
Nick Gubbins was the first wicket to fall, after a positive start with seven boundaries, trapped lbw by Ben Sanderson and Sanderson returned after lunch with a beauty that seamed back late to clip Morgan's off-stump.
At that stage, Middlesex were 79 for 5 and in danger of being blown away but Max Holden, familiar with Wantage Road after a loan spell last season, found a partnership of 69 with Robbie White either side of a rain delay to reduce the deficit.
The stand could have been ended before it began had Richard Levi held White on 5 down by his left boot. But the miss allowed a comeback of sorts before Holden, having nudged and poked 30 from 76 balls, edged Brett Hutton behind just before bad light brought tea 18 minutes early.
Then Nathan Buck began an at-times unplayable spell to end the innings. A snorter climbed on White to take an edge behind and he fell for 35 - the second-top score in the innings after the 37 extras included 22 byes.
Another lifting delivery took the gloves of James Fuller and rebounded into the stumps. James Harris battled away for 32 balls for 6 but was lured into driving and skewed a catch to point before Tim Murtagh, attempting a third leg-side heaved having struck a six then four, got a thin edge to wicketkeeper Ricardo Vasconcelos.
With Middlesex 159 behind and with 29 overs left in the day, Alex Wakely enforced the follow-on and Sanderson trapped Gubbins lbw for the second time in the day - the batsman clearly unhappy with the decision - before bad light took out the final 18 overs of the day.