Their 183-run fourth-wicket stand lifted West Indies to 288 for four in their first innings, still 219 runs behind England at stumps.
Blackwood, who would have gone lbw for a duck if England had reviewed the not out decision, finally went shortly before the close for 102, plumb lbw when not offering a shot to Dan Lawrence.
Key innings from both Brathwaite & Blackwood on Day 3.?? #WIvENG https://t.co/x0fSvPJ640
— Windies Cricket (@windiescricket) 1647639965000
But Barbadian Brathwaite was an immovable object as he played with the utmost of caution in taking 278 balls to reach his 10th Test century.
He was especially proud to reach his ton in front of his mother at his home ground and received a warm ovation all round, even from many England fans in a mostly full Kensington Oval.
Opener Brathwaite has been on the field for every minute of the first three days, displaying a powerful sense of concentration that has never wavered.
He was 109 from 337 balls at stumps, with nightwatchman Alzarri Joseph on four.
153* run partnership off 348 balls!???? #WIvENG https://t.co/vIWbm9lnTQ
— Windies Cricket (@windiescricket) 1647635111000
“This one means a lot,” Brathwaite said. “My mother was here. She’s never watched me play a game before. It was amazing man.
“It’s still a decent pitch to be honest, one or two (balls keeping) a little low.
“Tomorrow’s crucial again. The more time we can bat the better for us. We still are a ways off their total and have to work extremely hard tomorrow.”
Although he has a mediocre batting average of barely 33, Brathwaite has been a West Indies mainstay for more than a decade and knows how to occupy the crease.
He was supported on Friday by a sometimes fortunate Blackwood, who should have been sent packing twice and England both times had only themselves to blame.
The Jamaican was rapped on the pad by Ben Stokes for what would have been a duck, but England erred in opting not to review the on-field not out call because ball-tracking showed it would have hit the middle of leg stump.
Test Ton #3️⃣!?? Well played @JBlackwood100.?? #WIvENG #MenInMaroon https://t.co/9wOw68rYHJ
— Windies Cricket (@windiescricket) 1647637225000
Blackwood had another life on 65 when bowled by a yorker, a no-ball call foiling what would have been debutant Saqib Mahmood’s first Test wicket.
The England bowlers toiled honestly but lacked the cutting-edge penetration needed to beat the bat regularly on a placid pitch, with none of their pacemen averaging much more than 80 miles-per-hour (130 kph).
Spinner Jack Leach sent down 44 tidy overs, landing the ball on a proverbial dinner plate with monotonous regularity but only occasionally beating the bat.
He should have had Brathwaite stumped shortly before the close but it was Blackwood who fell to Lawrence, a late reward for England after hours of fruitless toil.
After last week’s first Test in the three-match series was drawn, the current contest also seems most likely to end in a stalemate unless England can pick up some quick wickets on Saturday morning.