Nottinghamshire 177 (Porter 4-50) and 116 for 1 (Slater 54, Brathwaite 47*) lead Essex 233 (Vijay 56, Harmer 48, Mullaney 4-68) by 60 runs
Batting for a second time, 56 runs adrift, the home county's opening pair reproduced last week's heroics with a century stand to help Notts towards 116 for one by the close, a lead of 60.
A week ago, in the drawn Yorkshire fixture, Brathwaite and Slater compiled stands of 182 and 91 on their home debuts.
They were parted in the first over on the opening day of this match but rediscovered their mojo to blunt the Essex attack for more than two hours. Slater, who scored 109 against the White Rose, made 54 before being dismissed just before the close. Brathwaite remains undefeated on 47.
Earlier, the visitors were bowled out for 233 before tea, with captain Steven Mullaney taking four for 68, his best figures of the season.
Resuming after lunch, from 133 for five, after rain had wiped out the entire morning session, the reigning county champions lost Jamie Porter in the first over of the day, lbw to Luke Fletcher.
The same bowler then had Adam Wheater spilled twice in the slip cordon but the batsman couldn't make the most of his good fortune by then nicking Mullaney behind for 14.
Ryan ten Doeschate took his side to within three of the Notts' first innings score before falling lbw to Mullaney for 32.
Emulating Nottinghamshire's tail-wagging exploits of the opening day, Essex's last couple of wickets helped themselves to some unexpected but welcome runs.
Simon Harmer received good support from both Matt Coles and Matt Quinn as the last two wickets added a further 59.
Luke Wood eventually finished things off, trapping Coles lbw for nine, before inducing Harmer to chop on for a well-constructed 48, leaving Quinn unbeaten on one after 33 minutes at the crease.
Slater had an early scare when he nicked Porter at the start of Nottinghamshire's second innings but Dan Lawrence, at third slip, could only parry the ball away at full stretch.
Chances from then on were few and far between as the deficit was wiped out without too much inconvenience.
Slater's 50 was reached from 83 balls faced but he failed to see out the day after being struck on the pads by Coles.
Fletcher, in as Nottinghamshire's nightwatchman, was spilled by Murali Vijay in the final over of the day but Brathwaite, who has registered half-centuries in each of his first two outings for Notts, will resume on the third morning within three runs of extending that sequence.