Surrey continue to keep Stuart Meaker, their quickest bowler, in reserve as Gareth Batty continues. An inside edge by Jonny Bairstow flies off the keeper's gloves and he takes a fortuitous single. Just three from the over.

A bouncer from Tom Curran surprises Jonny Bairstow, who collects four via a top edge over the keeper's head as he tries to hook. A long-hop later in the over is despatched through mid-wicket in more orthodox fashion, and that's a more productive over for Yorkshire. 

Jonny Bairstow tries to sweep, gets a top edge and is very lucky to see the ball fall into the gap between two fielders. The score is moving forward at a steady crawl at the moment - only 20 off the last seven overs.

Another excellent over by Tom Curran, with only a single by Gary Ballance denying him a maiden. Jonny Bairstow appears to be timing it well, but has yet to pierce the field.

As Jack Nicholson said in The Shining, 'here's Jonny'. England's Mr Bairstow is immediately under way with a couple of singles, but Surrey will be delighted with their second success, ending a stand of 44 between Alex Lees and Gary Ballance.

Don't forget that Warwickshire meet Somerset in the second semi-final tomorrow and we will have full coverage for you from about 10:40 BST.

The name of the game is 'bide your time' for Yorkshire. It's a good over by Tom Curran, yielding a solitary single to Gary Ballance. 

Gary Ballance brings up Yorkshire's 50 with a single through the covers. But Alex Lees errs on the side of caution after Gareth Batty turns one prodigiously past the outside edge.

Tom Curran relieves his younger sibling, whose first five overs cost 18 runs. Elbows pumping behind him, he finds a decent rhythm, conceding only four singles. 

Here is that first bowling change and Surrey skipper Gareth Batty brings himself into the attack with his off-spin. Like Azeem Rafiq earlier in the game, he finds a little turn but Alex Lees plays to mid-on for a smartly run single. Gary Ballance plays across the line to the last one, but the resulting outside edge does not go aerial.

No bowling change yet from Gareth Batty and it's another boundary for Yorkshire as Sam Curran drops short and Alex Lees pulls over mid-wicket. That's the end of the first powerplay - at the same stage Surrey were 38-2.

Back-to-back boundaries for Alex Lees as Jade Dernbach gives him too much room outside off-stump. Dernbach decides to go round the wicket and Lees is beaten as he swishes at the final delivery.

Sam Curran sends down a well-directed bouncer but Gary Ballance plays it well, keeping his eyes on it and swaying back out of harm's way. The left-hander takes a single, but partner Alex Lees is beaten outside off stump as he plays an airy waft on no great distinction before a misfield by Curran's brother Tom gifts him a couple of runs.

A wide half-volley by Jade Dernbach allows Gary Ballance to flay the ball through the covers for four. Other than that, it's another respectable over for Surrey.

Yorkshire captain Alex Lees has had a dismal time of it in the One-Day Cup this summer with only 108 runs in nine matches at an average of 13.50. Is today the day he comes good?

He forces through the covers for two in Sam Curran's latest over, but the other five balls are dots.

Image source, PA

Gary Ballance really does go a long way back in his crease. It's amazing he doesn't tread on his stumps. Jade Dernbach keeps him pinned down with accurate bowling before a wide one allows Ballance to slash over gully for four.

Sam Curran isn't the quickest bowler around, but he is lively enough from a bustling run-up. After a first-ball wide, he yields only one single from the over.

Gary Ballance nudges his first run off his hip to end the over, but it's been a really good one for Surrey with Yorkshire's leading One-Day Cup scorer back in the dressing room.

It's left-armer Sam Curran from the other end and he goes past the outside edge of Alex Lees' bat with one that leaves him through the air. Lees eases one through the off-side field to get off the mark with a couple before collecting his first four with an extra cover drive.