Essex 263 (Allison 69*, Westley 58, Browne 49, Taylor 4-59) and 63 for 5 (Critchley 14*, Pepper 7*, White 2-12, Sanderson 2-22) lead Northamptonshire 163 (Young 37, Allison 5-32) by 163 runs
Sanderson struck twice early in Essex's second innings to account for Sir Alastair Cook and Tom Westley in consecutive maiden overs. White also picked up a wicket in successive overs to reduce the Eagles to 52 for 5 and snatch back the momentum after the hosts had conceded a first innings deficit of 100.
Earlier Essex seamer Ben Allison returned career-best bowling figures of 5 for 32 as Northamptonshire were bundled out for 163. Allison's maiden five wicket haul followed his heroics with the bat yesterday when he registered his highest score of 69 not out. With Shane Snater also taking two scalps, Northamptonshire lost their last five wickets for 16 runs.
When bad light prompted an early finish Essex were 63 for 5, a lead of 163, which sets up an intriguing final day.
In the morning session, Will Young (37) and Luke Procter made a solid start extending their overnight partnership to 39, before Allison found some extra bounce to take Young's glove with keeper Michael Pepper taking the catch.
Rob Keogh started brightly, playing a conventional sweep and reverse sweep off Simon Harmer for consecutive boundaries before the South African spinner spun one back to hit the stumps.
Procter cut Allison crisply for a boundary and had advanced to 28 when he played down the on-side to the same bowler and was well caught low down at leg slip by Matt Critchley.
Saif Zaib (18) played some attacking shots either side of lunch including a back-foot punch off Allison for four and a blow over extra cover off Harmer. But after driving Snater through cover to the ropes, he edged Snater's next delivery to Harmer at second slip.
It precipitated a lower-order collapse as Northamptonshire fell from 147 for 5 to 163 all out. Two balls after Zaib's wicket, Tom Taylor edged a well-directed short ball from Snater through to Pepper.
Allison was back in the action with some sharp work in the field to run out Gareth Berg before angling one back in to castle Sanderson.
James Sales struck four boundaries in his 28 to ensure Northamptonshire passed 150. He had an early reprieve when Harmer put him down at second slip, taking a blow to his spinning fingers in the process and requiring attention from the Essex physio. However the young all-rounder eventually became Allison's fifth victim when he edged to Cook at slip.
With the bat, Cook (10) offered two chances to the slips on 0 and 2 but both were missed by Emilio Gay and Young. He was out shortly afterwards when he drilled Sanderson straight to Taylor at cover. It meant he missed out by 34 runs on 1,000 for the season. In his next over Sanderson trapped Tom Westey lbw to leave Essex 23 for 2.
Nick Browne (18) looked solid throughout a lengthy stay at the crease, but after facing 63 balls Taylor got one to jag back and knock over his middle stump.
Dan Lawrence walked to the crease on a king pair and played and missed to his first ball from Sanderson. He looked skittish early on but started to settle, taking consecutive boundaries off Berg. His downfall came thanks to an ugly looking cut shot off White which flew to Gay who took a stunning diving catch at second slip.
White struck again in his next over when he got one to jag back and knock over Feroze Khushi's stumps, but Matt Critchley, who played some pleasant shots including a drive straight down the ground off Taylor, was unbeaten on 14 at stumps.
On a day of presentations, Procter was named player of the year by the Northamptonshire Supporters' Club and presented with his award at lunch. He has so far scored 959 runs at an average of 56.41 this season with one innings left to bat in this match..
At tea Adam Rossington, who skippered Northamptonshire to promotion in 2019, was given a special presentation by the club to mark his eight years of service. He joined Essex on loan earlier this season ahead of signing a permanent deal.