Cilic hauls himself back from 0-30 to 30-30 with the help of an ace down the 'T' - only his fourth of the tournament. Another howitzer from the Croat? Wawrinka doesn't think so... der-dum... der-dum... and neither does Hawk-Eye. Second serve finds the target and Cilic collects another point. In the end, it is a straightforward hold. Ivanisevic applauds on the sidelines. Is the US Open champion preparing a fightback?

We've been asking who you can see breaking into the top level of world tennis:

Bob in Spain:, external Watch out for Borna Coric as a future top player. Already ranked 89 in the world and turning 18 today.

John McEnerney:, external If Rod Laver, Pat Cash, Hewitt & The Woodies all gave Tomic a good clip around the ear & kick in the pants he could rule tennis!

Kayley Jay:, external David Goffin should do well - hopefully he won't get injured again! I'd like to see him make another good run. Top 10 next year?

Image source, Getty Images

Easy peasy. 'Set Point' flashes up on the advertising boards around the court as Wawrinka advances to a 40-0 lead. Cute from the Swiss, who drags Cilic towards the tape with a drop shot and simply watches his opponent push his volley into the tramlines.

Piers Newbery
BBC Sport at the O2 Arena in London

Image source, Getty Images

"The tennis might have been fairly underwhelming so far but the staging has once again impressed, and another 17,000 spectators are packed into the O2 this evening. The venue has one year left before the rival cities can make a bid to take the tournament away - something that would surprise John McEnroe.

"'You're asking someone who grew up in New York, who used to play what I considered one of the great events in Madison Square Garden,' said the American. 'They should never, ever have left there. Having said that, this has been clearly the most successful of all the six or seven locations that have been since we left Madison Square Garden. It would be hard-pressed for me to imagine not having it either here or there.'"

"Thank you," says the umpire in an attempt to quieten one or two distant cries from those in the vertigo-inducing seats. Wawrinka soon has the crowd purring with a forehand winner which fizzes by Cilic on the opening point. At 15-15, Cilic is undone by a Wawrinka lob. It was the Croat's poor approach play, rather than Wawrinka's brilliance, which killed him off on that point. Wawrinka not firing on all cylinders but it might be good enough to see off Cilic.

To deuce we go, but neither player wants to take the upper hand. It's itsy and it's bitsy. Cilic, though, comes through, Wawrinka putting a touch too much juice on his returns.

David Law
BBC Radio 5 live sports extra commentator

"Coming into the foyer this evening, it was very busy as there were 17,000 people here for the tennis, and a lot of people rather alarmingly dressed for an evening at the local nightclub. They get a bit rowdy inside the O2 here too, the evening sessions are rather different to the afternoon when people are a little more polite."

A series of errors from Wawrinka allows Cilic to work his way back from 30-0 to 30-30. But the Croat goes on to net a return on the next point and follows that up by sending another beyond the baseline. A messy hold, but Wawrinka is set to nudge ahead in this match.

We've been asking who you can see breaking into the top level of world tennis:

Max, Nottingham: Dimitrov has all the attributes of a future legend. All he needs is a physical change much like Murray went through around the same age. With Roger Rasheed training him, it's a matter of 'when' rather than 'if'. I'm excited!

Image source, Getty Images

Keith Punter:, external US Open champion or not, Cilic has sadly been out of his depth this week.

For those interested, Cilic is wearing a cobalt blue t-shirt and daffodil yellow trainers. The US Open champion's hands are as delicate as a petal at the net, too, as he exchanges volleys with Wawrinka before responding to a lob with an overhead.

At 30-30, the game could swing either way, but Cilic floors Wawrinka with a booming serve and holds thanks to a textbook serve and volley. Nothing more to see here.

A double fault. An ace. A stonking single-handed backhand winner down the line. An iffy backhand into the tramlines. Wawrinka up and then down, or down and then up, in this game. Cilic forces the game to deuce, before Wawrinka sees off the challenge with a sweet serve and volley.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

"Kei Nishikori is someone who can get close to the top players, and it will be interesting to see how Grigor Dimitrov develops - he's a lot like a young Roger Federer, he has a good coaching set-up and has a lot of hunger."

Who can you see breaking into the top level of world tennis? Text and tweet us with your thoughts.

Gasps from the crowd as Wawrinka returns a Cilic serve with the speed of a Cobra's tongue. Brilliant from the Australian Open champion. He fetches and retrieves from the baseline, defending stoutly, before Cilic falters - presenting his opponent with three break points. The Croat saves one, but approaches the net and volleys into the tramlines on the next point. A break of serve, a third game in the bag, and Wawrinka is through to the semi-finals.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

Image source, Getty Images

"Wawrinka leapt onto that forehand and clubbed it down the line. Great tennis."

Solid serving once again from Wawrinka. A serve and volley eases him to 40-0. Cilic absorbs the punches on the next point, though, counter-attacking with another thunderous forehand down the line and Wawrinka's response is to overcook a forehand. Again, Cilic nicks just the one point on the Wawrinka serve, the Swiss ending the match with a picture-perfect forehand winner which grazes the tramline.

Leon Smith
GB Davis Cup captain on BBC Radio 5 live sports extra

"This is a terrific tournament, it's more like the Davis Cup and much better for the spectators."

Both players unleashing the big shots early. Cilic with a forehand down the line, Wawrinka challenges the call, but replays show the Croat kissed the line by 0.000001mm. Close. To 40-15 we go and it's a routine hold for the US Open champion. This could actually be a contest.

David Law
BBC Radio 5 live sports extra commentator

"If nothing else tonight, this crowd deserves to see the best of Marin Cilic - it deserves to see the US Open champion playing like the US Open champion."

Wawrinka sprints towards the back of the court to start this match. Eager. The Swiss made a fabulous start to this tournament, securing a sensational 6-1 6-1 victory over Berdych. Then he came up against Novak Djokovic and lost 6-3 6-0, but everyone seems to lose to the world number one these days so it should have no bearing on the outcome of this contest.

Two easy points for the Australian Open champion before he notches a third with a fabulous forehand winner into the corner. Wawrinka's single-handed backhand falters, gifting Cilic his first point of the game, but there's no danger of the Croat overhauling Wawrinka from here. Game Wawrinka. Two more and the Swiss is through to the last four.

There'll be no more of Tomas Berdych at the 02 this year as two defeats in Group A means the Czech it outta here. The sixth seed has tweeted: , external"I had great year 2014. Thanx to my team, fans for your fantastic support in good and bad times!!! With ❤️ Tomas"