Essex must score 400 at Northants to stay in title hunt
When Essex started their first innings, they needed at least 400 if Surrey were bowled out at Southampton for less than 250.
Sanderson (3-15) removed Alastair Cook, Nick Browne, and Dan Lawrence in nine overs while conceding just 14 runs.
After Surrey collapsed at the Ageas Bowl, they rallied to 125-4 by close of play, still 244 runs behind but requiring only a draw to win the County Championship.
In order to win the match, Essex needs Hampshire to beat Surrey and then earn four batting points on Thursday.
Before he was adjudged LBW to Umesh Yadav for 172 off 167 balls, Northamptonshire centurion Rob Keogh moved past his previous highest score of 161 at Wantage Road.
When Broad smashed Jamie Porter down the ground for four, he posted his maiden first-class half-century, supporting Keogh in a 98-run partnership in 20 overs.
The other end continued to lose wickets. In his final match for Northamptonshire before moving to newly-promoted Worcestershire, Tom Taylor smashed Matt Critchley for six, but he was unable to repeat the shot, picking out Porter at mid-on.
After Porter got the new ball to seam back and knock Sanderson’s middle stump out of the ground, White edged and Cook took a tumbling catch at slip.
Lewis McManus caught Browne behind for 13 after he drove loosely to a fuller ball from Sanderson.