Sanderson’s haul included the wicket of former England skipper Alastair Cook, which was the 300th wicket of the 33-year-old’s impressive first-class career.
It was a day that definitely belonged to Northants, who started the day on 233 for seven.
Procter and Gareth Berg, who hit a superb 75, saw the County to a big first innings total, and then out-of-sorts Essex crumbled under the Northants’ bowling pressure.
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Sanderson ended the day with four for 24 from 16 superb overs, while Matt Kelly claimed two for 31, and there was a wicket apiece for Tom Taylor and batting star Procter.
“We spoke in the morning in the huddle about Procter going on and trying to get a big one and backing up with the other batsmen we had left,” said Northants assistant coach Liddle. "And praise to Procky, he was fantastic.
"Then with the ball, each bowler backed up each other and we were relentless in the line and length we wanted to bowl.
"It’s been a great day for us and exactly what we discussed in the huddle this morning, so a pat on the back for all the lads in there.
“Everyone is putting their hands up at key moments for us, long may that continue. "We’re definitely in the box seat and we’re happy at how today’s gone for us.”
Liddle is also the Northants bowling coach and he had some words of special praise for Sanderson.
“Sando’s bowling in county cricket is next level,” he said. “He does it week in week out. Credit to him. He turns up and puts the overs in.
"It’s a great story: one of England’s greatest batsmen is his 300th wicket today.”
Northants will now be hoping to drive home their considerable advantage on Saturday morning, and Liddle said: “Our first priority is to get those two wickets in the morning, then we will reassess what we want to do.
"But it is important we go about our business as we have done tonight and turn up in the morning and really get stuck in.”