James Anderson hopes England team-mate Dom Sibley can go on to nail down a future in Test cricket after proving his credentials with a knock of real substance in Cape Town.

Sibley's first six attempts at the highest level had yielded just 105 runs but he knuckled down for nearly six hours and 222 deliveries as he ground down the South African attack for an unbeaten 85 on day three of the second Test, leaving the tourists 264 ahead at Newlands.

It was an obdurate, unflashy and deeply important innings in the context of the match, the series at large and Sibley's own journey. Another 15 runs when play resumes on Monday and it may go down as the launching point for a long and fruitful spell heading up the England order.

Their task will be to push the lead up past 350 before handing back to Anderson as England look to square the series at 1-1 with two to play.

And, after missing five months with a calf injury prior to this trip, the veteran is more than happy to take up the battle.

"I sat down at the end of day two and that feeling is what I'd missed: that proper hard day of Test cricket, that proper graft," he said having capped off outstanding figures of five for 40.

"That's why I still want to play cricket, that's what I get a buzz off...coming off the field after a day like that. It was a pretty hot day as well, so you're sweaty and you know you've put a shift in."

Proteas coach Mark Boucher has not yet given up hope of turning things around, particularly after an unexpectedly benign showing from the Newlands pitch, but accepts his side are in a corner.

"Our backs are up against it to be honest," he admitted.

"After the first two days I wouldn't have wanted to chase any more than 250 but, having looked at the way the wicket played and the way it flattened out quite a bit...if we can chase anything around 330, 340 then great.

"We've got to believe a couple of our batters can get a big hundred."