Lancashire 207 and 82 for 1 (Jennings 45*, Bohannon 28*) lead Essex 219 (Critchley 78, Anderson 4-70) by 70 runs
Critchley was last man out for 78 from 154 balls to follow scores of 55 and 53 in last week's win at Lord's against Middlesex. It enabled Essex to post 219 and eke out a 12-run advantage that at one time in the day looked beyond them.
Anderson had been almost unplayable in the first hour under slate-grey clouds as he extracted pace and movement from a pitch that had other batters looking like mere mortals. One ball was so full of life and pace that it beat wicketkeeper George Bell's extravagant dive and raced away for four byes.
Adam Rossington - who later gave up the wicketkeeping gloves in Lancashire's second innings to Michael Pepper after damaging a hand - lasted just eight balls before he gave a thick edge to another lifter from Anderson and Luke Wells held on above his right shoulder.
A third Essex wicket fell in the first half-hour when Simon Harmer, on nought, fenced at Tom Bailey and Wells snaffled again at first slip.
Critchley, who had struggled for consistency last season after his move from Derbyshire, continued to hold up the other end and reached his latest fifty from 100 balls. He played first fiddle in a seventh-wicket stand of 43 in 12 overs with Doug Bracewell, though he was fortunate when dropped by Wells on 53. The enterprising partnership ended when Bracewell chased a wide ball from fellow New Zealander Will Williams and became the fourth slip catch of the morning.
When Anderson was rested after a six-over burst worth 2 for 20, it gave Essex some respite and Critchley took advantage by nonchalantly angling Williams past the slips for one of his nine fours.
When Anderson did return after the first of three rain breaks, there was not the same venom or spite in his deliveries. Indeed, tail-ender Sam Cook played two controlled drives to the boundary at third off England's premier strike bowler in a pleasing cameo worth 20.
The eighth-wicket pair put on 38 valuable runs that took Essex beyond Lancashire's first-innings total of 209, but it ended when Cook dollied Colin de Grandhomme to midwicket. Essex were all out soon after when Critchley holed out to deep extra cover to give Williams a third wicket.
Lancashire had reached equality when Wells departed for his second single-digit score of the game, going half-forward to Jamie Porter and being judged lbw.
However, that brought Bohannon in to join Jennings and the pair patiently pieced together a half-century stand in 16 overs that was embroidered by some loose bowling from Bracewell, who was taken off after conceding a combined total of 24 runs from his third and fourth overs.