Northants up against it at Somerset as England man Overton strikes
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Having extended their first innings total from an overnight 271 for four to 389 all out, the hosts reduced the County to 184 for six in reply, which was a decent effort having collapsed to 37 for four.
Overton ended the day with four for 25 from 13 overs.
But both were upstaged by Overton, who worked up good pace from the Marcus Trescothick Pavilion End, having missed the last two Championship matches through international duty and then a back problem.
Skipper Will Young kept Northamptonshire in the game with a defiant 85, but found little support of the rest of his team's top six, who mustered just 37 between them.
Somerset began the day cautiously at the Cooper Associates County Ground, showing no inclination to chase the 79 runs in 14 overs that would have yielded four batting points.
Lewis Goldsworthy had not added to his overnight 22 in 6.4 overs when edging a defensive shot to first slip off White with the total on 284.
James Rew finally broke loose with successive boundaries off White to bring up the 300 and a third bonus point in the 107th over.
The young wicketkeeper fell lbw to Tom Taylor on 32 and Overton also departed in the morning session, stumped advancing down the pitch to Keogh, having made 13.
At lunch, Somerset were 362 for seven, having scored 91 in 31 overs. Lewis Gregory was 27 not out and added five after the interval before being pinned leg before on the back foot by White.
Sajid Khan and last man Kasey Aldridge perished in the bid to accelerate, skying shots to White and Josh Cobb respectively, who both held testing catches.
The Northants reply had reached 16 when Emilio Gay feathered a catch to Rew off Josh Davey, who quickly followed up by having Luke Procter pouched by Overton at second slip.
Davey almost claimed a third wicket when Cobb chipped a catch to mid-on, but had overstepped and was called for a no-ball.
Overton had not been given the new ball, but his introduction to the attack soon reaped dividends as Cobb fended a sharply rising delivery to short leg to make in 29 for three.
The visitors were in a hole eight runs later when Keogh was caught behind off Overton trying to withdraw his bat.
But Will Young held firm and was unbeaten on 40 at tea, which was taken at 73 for four.
The Northamptonshire skipper moved to an excellent 50, off 88 balls, with 10 fours.
Overton had resumed the attack at the start of the final session and produced a quick delivery to have Ricardo Vasconcelos, on 17, caught behind by Rew reaching above his head.
The England seamer, perhaps still mindful of his recent back spasms, was then immediately replaced by the expensive Aldridge, whose first seven overs, in two spells, went for 42 runs.
Somerset’s grip appeared to be loosening as Saif Zaib helped Young add 63 for the sixth wicket.
But back came Overton for a third spell to claim another key scalp.
Having faced 153 balls and extended his boundary count to 15, Young edged a defensive push to second slip where Tom Abell held a comfortable catch.
At 158 for six, Northants still needed 82 to avoid the prospect of following on. Zaib survived a testing examination from Overton to be unbeaten on 27 at the close, with Taylor 19 not out in a stand worth 26.