Annabel Croft
Former British number one on BBC Radio 5 Live

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Siegemund strikes me as someone who very quickly puts a point behind her that she's lost. She walks away very quickly, turns her back on the point and starts to re-focus on what is ahead of her.

Aryna Sabalenka left the court at the end of the second set and was followed a short while later by Laura Siegemund.

So there will be a slight delay before the decider gets under way.

Taylor Fritz was within touching distance of multiple match points. He moved quickly in to pounce on a forehand winner before Karen Khachanov blasts a forehand long for 0-30.

However, he buries a tame forehand in the net before Karen Khachanov stretches for a forehand volley to level the game at 30-30.

Winning the next two points to hold serve, Khachanov lets out a roar.

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Aryna Sabalenka has levelled it up.

Excellent response from the world number one, both to dropping a set down and then to Laura Siegemund breaking back early in the second.

It's a lengthy game but Sabalenka eventually breaks when Siegemund dumps one into the net.

The top seed has to be the favourite from here. Siegemund has dropped a set for the first time at the Championships.

Tracy Austin
Two-time Grand Slam champion on BBC One

It is so fascinating to watch Laura Siegemund. She is a rhythm buster. You very rarely see her hit the same two shots in a row.

Sabalenka has taken a bit of pace off her returns which allowed Siegemund to nail her drop shots.

Laura Siegemund is not the quickest between points and you can tell it is irritating Aryna Sabalenka a bit.

However, she takes that frustration out on a vicious forehand, drive into the corner to save a game point.

It all comes flooding back when she goes long on a set point, though.

Taylor Fritz has rediscovered his first serve and he's rediscovered his range.

He seals back-to-back holds to love with an emphatic smash at the net.

That's an absolutely lovely shot - possibly the shot of the match so far.

Karen Khachanov crouches down low to receive a cross-court backhand which just dipped over the net and responds with a cute sliced backhand drop shot for 30-0.

A double-fault at 40-0 brings a rueful shake of the head but it's a momentary blip.

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That game whistled by. Fritz holds to love, scarcely breaking a sweat.

His first serve percentage, which was 38% in the third set, is a far healthier 81% in the fourth.

Tracy Austin
Two-time Grand Slam champion on BBC One

What an effort from Sabalenka after some fatiguing points. It is tough to hit a winner against Siegemund because her anticipation is so good.

These new balls are much sleeker and will be moving quicker through the air.

Eight strips of alternating dark and light grass make up each service box. One of Karen Khachanov's serves is an entire strip wide.

With an ugly cross-court heave which clips the line, Taylor Fritz pegs the score back to 30-15, but on the next point, Khachanov toys with him like a puppet on a string. He drags the American into the net with a drop shot before nailing an inch-perfect lob. Fritz gets his racquet on it but his return balloons long.

Khachanov holds to 15.

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Aryna Sabalenka is getting louder and louder on Centre Court and lets out a huge roar after saving a break point.

What a point it was, too! Both players dragged this way and that before Sabalenka thumps an overhead smash beyond Laura Siegemund.

A driven forehand then has too much for Siegemund and Sabalenka holds.

Sam Smith
Former British number one on BBC One

The tiger is roaring. It will feel good for Sabalenka to be hitting winners. I can't believe she has not hit an ace in this entire match so far.

Siegemund is under siege from Sabalenka in this game.

Three games in a row for Taylor Fritz.

He holds to 30, sealing the game with an ace down the T.

Sir Ian McKellen (or Gandalf to fans of the Lord of the Rings films) is keeping a close eye on proceedings from the Royal Box on Centre Court where top women's seed Aryna Sabalenka is a set down to world number 104 Laura Siegemund...

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Tracy Austin
Two-time Grand Slam champion on BBC One

That is a massive game and it will give Sabalenka so much momentum.

There is a huge power difference between the two players. Siegemund's first serve is about 54 percent down the middle of the box.

Sabalenka has taken a little bit of speed off her returns to make sure that more go in. She is looking for more consistency than power. Good patience from her.

Image source, EPA

Big moment.

Aryna Sabalenka comes back from 40-0 down to go a break up again in this second set.

It's frustration for Laura Siegemund, who double faulted to make it 40-15 and then failed to put away a passing shot at 40-30.

Sabalenka uses her power well, though, and moves her opponent side to side before Siegemund's backhand sails long to give the top seed the break.

We're back on serve in the fourth set.

Karen Khachanov saves the first break point but hits his backhand wide to give up the second. Taylor Fritz slipped a couple of times on the backhand side during that game and Khachanov lost the point both times.

Taylor Fritz is beginning to purr. A gorgeous down the line backhand gives him 0-15 before Karen Khachanov fails to capitalise on his opponent slipping, underhitting a cute shot into the net.

The Russian hits back with an ace but now finds himself facing two break points.