Josh Hazlewood replaces Mitchell Starc but there's still not a huge amount happening for the bowlers.

Three from the over, all for Ryan Rickelton, with two coming as he guides the ball just wide of gully.

Nathan Lyon will continue from the other end.

I'd agree with that, Ant. Anything over 150 could make for an interesting chase but Australia would still go in as big favourites.

Three from Nathan Lyon's latest, with some good, positive running earning Matthew Breetzke a quick single.

Half an hour into day four and it's been a steady start, just 14 runs and no wickets but the situation and the tension has made it extremely watchable.

Change of angle from Mitchell Starc a couple of balls into the over, going round to Matthew Breetzke.

The Aussie quick bangs in another bouncer soon after and Breetkze easily ducks under it then stays on his haunches looking at Starc.

Eventually he gets up and sticks his tongue out at Starc. The bowler isn't overly impressed and there are a few words at the end of the over.

That didn't take long.

Top shot from Ryan Rickelton.

He goes back, deep into his crease to create the length and punches Nathan Lyon through the covers for the first boundary of the morning.

The umpire steps in for a quick word with Mitchell Starc, I'm not sure if that is to do with his follow through - he's close to that danger area - or the way he kicks at the crease.

Either way, if Starc is trying to do anything to help Nathan Lyon, it's worth remembering that South Africa spinner Simon Harmer could also benefit later in the game.

Australia were as high as 70% on WinViz yesterday. This is the current reading...

Image source, CricViz

Slightly nervy moment for South Africa as Ryan Rickelton clips towards mid-on and calls for a single.

It should be routine enough but Matthew Breetzke gets stuck behind bowler Nathan Lyon for a moment and ends up having to sprint through to make his ground.

The right-hander then ends the over with a fairly agricultural hack. Not pretty but it brings him two to deep mid-wicket.

Image source, Getty Images

Two from Mitchell Starc's over with Matthew Breetzke taking on a short ball but plinking a pull shot to square leg before Ryan Rickelton drives out to deep point for one.

Just that single from the first over of day four. Not much by way of outrageous turn for Nathan Lyon in that over but that is expected to change as the day goes on.

Footmarks created by the left-arm quicks means it's the right-handed batters most likely to be tested.

That means left-hander Ryan Rickelton's wicket is even more crucial for South Africa.

Anyway, speaking of left-arm quicks, here's Mitchell Starc.

Slip, leg slip, silly point and short leg all in place as Nathan Lyon gets things started.

Matthew Breetzke blocks the off-spinner's first ball solidly before pushing the next into the covers for a single.

South Africa are up and running on day four.

The umpires are making their way to the middle and South Africa batters Matthew Breetzke and Ryan Rickelton are not far behind them.

It's a bright, sunny day in Cape Town and there can be no better setting than Newlands for this tussle between two titans of Test cricket.

The Australians are out now as well and Nathan Lyon will bowl the first over of the day...

Image source, Getty Images

Here we are then, day four of this all-important third Test - and the series could be decided today.

Australia will certainly hope so. South Africa will resume on 140-4 at Newlands, leading by just 40, and a couple of early wickets would put the tourists firmly on top.

One ill-judged swipe from Temba Bavuma late on day three means the Aussie already have the upper hand but, on a deteriorating pitch, if the Proteas can extend that lead towards 200 then things could get very interesting.

So settle in, the first ball of the morning is just a few moments away...