Essex 249 for 4 (Walter 80*, Critchley 51*, Potts 2-65) trail Durham 587 (Robinson 198, Lees 113, Ackermann 73, Critchley 4-158) by 338 runs
Paul Walter and Matt Critchley dug Essex out of trouble on day two of their Vitality County Championship run-fest with Durham.
Durham's fast bowling attack had restricted the hosts to 120 for 4 in response to 587, but Walter struck 80 not out and Critchley unbeaten 51. The duo put on 129 for the fifth wicket to close the day on 249 for four.
Earlier, Ollie Robinson had done his England Test hopes no harm with a flawless 198 as Durham secured maximum batting points in their title charge.
Durham, resuming on 445 for 4, continued to drown Essex's attack in runs - as they smashed 142 runs in 26 morning overs before they were bowled out - with maximum batting points pocketed.
Robinson completed his 150 with the third ball of the day - the last four of his nine career centuries have exceeded the milestone.
The former Kent man simply picked up where he had left off on day one, scoring runs at ease and refusing to allow the bowlers to build any pressure.
He passed his previous best of 171 - collected against Lancashire in May - and looked set for 200 before trying to force a cut shot but only edged behind. He was given a generous applause by the crowd on his return to the dressing room.
Otherwise, Critchley and Simon Harmer plugged away with semi-regular wickets amongst the flow of runs.
Harmer and bat-pad Nick Browne combined to dismiss Colin Ackermann and Bas de Leede, with the South African later bowling former team-mate Peter Siddle. The off-spinner returned 4 for 188, the most runs he had conceded in a Championship innings.
To go with Robinson, Critchley also snaffled Ben Raine and Matt Potts. Essex's spinners joining for figures of eight for 346 with Durham bowled out for 587 - the 15th highest score at Chelmsford.
After an energy-sapping 122 overs in the field, the hosts were lethargic with the bat. Browne had already survived being dropped at second slip on 12 when he tickled Potts behind in the sixth over.
Dean Elgar oozed elegance with seven fours in 40, in a 51-run stand with Tom Westley, but edge Siddle to first slip before Westley was leg before to Raine. Jordan Cox got a start but also fell before making a telling contribution - bowled by a jag backer from the energetic Potts. It left Essex 120 for 4 and starting to worry about the follow-on target.
But Critchley mimicked Alex Lees' controlling style, while Walter was closer to Robinson's aggression, to resuscitate the innings with a century partnership.
Walter was imperious in his decision-making, whether it was slog sweeping for six, clipping off his legs, touching to third or flashing outside off stump. The maximum took him to 2,000 first class runs before his half-century came up in 63 balls.
Walter and Critchley - whose fifty came in 111 deliveries - were unbreakable in the evening session, as Essex finally found a foothold in the match, but remain 188 runs shy of the follow-on.
