Graeme Smith
Ex-South Africa captain on BBC Test Match Special

It's been a riveting first hour. I think the advantage for England is Cook and Root are still there. South Africa would have targeted Cook initially, he's the guy that can bat for time, the concrete that holds the batting line-up together.

First change for South Africa. This will be important. Can the back-up bowlers match the excellence of Morkel and Philander?

Perhaps surprisingly De Plessis throws the ball to Duanne Olivier who was wicketless in the first innings.

He's starts off with wobble seam deliveries to see what movement he can get off the pitch but that's too straight. On the pads of Alastair Cook and four through mid-wicket. Now a drive for four from Cook! The boundaries start to flow.

11 from Olivier's first over.

Mark: England look fragile at every number…. This won’t last to tea. They are becoming reliant on key players AGAIN.

Francis Edwards: Might I just remind everyone S.A's three best bowlers over the last couple of years, Steyn, Abbott and Rabada, aren't playing.

Jonny C: Peter Siddle would do very well today. Not express pace but tight awkward probing lines and lengths.

Shot, Joe. The skipper gets off the mark with a solid drive down the drive for three. That's the way to play. Don't go too hard at the ball and work it into the outfield.

We've had a couple of boundaries this morning but I wouldn't say any of them have come off the middle of the bat. The best shots have been the calm pushes.

Geoffrey Boycott
Ex-England batsman on BBC Test Match Special

Cook's the key man for me. Joe Root is batting fantastically well but Cook has the mental capacity and discipline to bat all day. He's done it before.

South Africa have seen a couple of edges drop short so they've stuck Dean Elgar in under the lid close at third slip.

High class stuff from Philander and he finds Cook's outside edge but Elgar can't react quick enough and the ball is past him.

Classic Cook. Forget the last ball and clip the next one for a couple of the hip.

Image source, Reuters

Oscar Beardmore-Gray: End of the road for Jennings and Ballance surely? No bottle whatsoever

Grant: Jennings and Ballance are no Test players. Just because they do well in county cricket doesn't make then Test players. Both need to go.

Stuart Mitchell: That's the two batsmen we expected to get out cheaply. Now for the real battle - Cook and Root vs SA.

And here is the wicket of Gary Ballance. It required a review, moments after South Africa had just called for another unsuccessfully.

Excellent bowling. Excellent captaincy.

Cook has seen so many batsmen come and go at the top of the order in his 142 Tests. He'll stay calm and up to know has only offered one chance this morning but his false shot flew wide of gully.

"Catch!" Just short. Morkel finds Root's edge but the skipper's soft hands keep the ball low.

Morkel has his hands on his head.

Mason: We need to stick with an opener, whether it's Hameed or Jennings, for a long while so they can learn from Cook before he goes.

Rich H: England have a fragile top order. Root can't take the burden of captaincy as well as regular rescue missions. Hales and Bell in?

Andrew Steadman: I don't understand the constant calls for Hales, if there's a replacement it's Stoneman. He's a better First Class player.

This is outstanding bowling. The replays show that wicket of Ballance kept a little low and because Philander is bowling so accurately he's keeping lbw in play.

England's two men under pressure at the top of the order are back in the hutch. We always thought it would come down to Cook and Root and now they're at the crease.

This is the game right here.

Stephan Shemilt
BBC Sport at Trent Bridge

South Africa can't believe that. After one look at the replay, most were back in their fielding positions. Only when they saw the ball-tracking did they know, running around with arms outstretched, mobbing Philander.

Geoffrey Boycott
Ex-England batsman on BBC Test Match Special

Right back on the stumps and a ball keeping low... that was always going to be out.

Philander gets wayward for the first time this morning and the ball flicks Cook's pads and runs down to fine leg for leg byes. Four more to the total.

Huge appeal from Philander for lbw to Ballance! That's close. Another review! Big moments.

Image source, Getty Images

Stephan Shemilt
BBC Sport at Trent Bridge

Soon, an 'umpire's call' like that decision on Ballance will not result in a lost review for the side that called it. Therefore, are we likely to see captains being more willing to challenge the on-field umpire's decision? So many reviews are umpire's call, so if the skipper knows he's less likely to lose out, expect many more referrals.

Michael Vaughan
Ex-England captain on BBC Test Match Special

Every ball you're watching you're thinking something is going to happen, but the England guys are proud lads, they will want to show they have a bit of fight in them today.

Wow. That was closer than I thought. It hit Ballance high on the pad but he's back in his crease and ball tracking show the ball was just clipping the bails.

Luckily for Ballance it's umpires call and he survives.

Michael Vaughan
Ex-England captain on BBC Test Match Special

I wouldn't have wasted a review on this.

Morkel hits Balance on the pads. Not out says Paul Reifel. It looks a little high.

South Africa are confident. They call for a review.

Image source, Getty Images