Nkumbu Kandy:, external "All those who predicted Kei and Cilic to reach the finals raise your hands?"

David Dawber:, external "Cilic needs to win this match. He'll never play this well again. This is his only chance to win a Slam."

Jonathon Solomons:, external "A break isn't a break unless you hold your next service game, Cilic breaks Fed back."

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Federer has amassed 599 victories on hard courts and is hoping to become the first player to hit 600 in the Open Era. Will he achieve that feat today? Even at two sets down, it's difficult to dismiss the Swiss. "Yes," ooze some spectators as Federer skips along the baseline and thumps a return into a zany angle but Cilic has propellers in his trainers and lead in his racquet. He's overpowering and outhitting Federer, and he holds to 30.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

"That is not Roger wanted. He is going to have to really think about what his game plan is against Cilic. That has slowed down Federer, just when he was starting to have that strut about him. He needs a quick set here. He is 33, his opponent is 25. That break back changes the tone."

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Cilic gambling like a high roller at a Las Vegas casino and his numbers come in. Ding! Ding! Federer forehand long - double break points. Another scintillating return from Cilic, but Federer responds with a snappy volley. One break point saved. But can he dig deep to save another? No, no, no. Cilic with a fabulous backhand winner. A fist-pumper. We're back on serve. I'm not sure my nerves can take this.

Rory Richard Whyte:, external "Did I say Federer in four? My apologies; hard to type on this laptop. Federer in five."

Piers Newbery
BBC Sport at Flushing Meadows

"Kei Nishikori is briefly watching this semi-final unfold with John McEnroe on CBS coverage. 'Well, it's interesting,' he says. 'Roger is always my idol but I know Cilic is playing really well.'

"You can hear McEnroe's eyebrow angling upwards as he responds: 'It doesn't matter if you play a guy who's won 17 Grand Slam titles or a guy who's won zero?'"

Cilic nets his forehand on the opening point and the the decibels rise on Ashe. Those not in the know would think Federer had just collected match point. Clever returning from Federer, stepping in from the baseline, which means Cilic can't negotiate the barrier 0-30, and the New Yorkers are cock-a-hoop about that.

But their joy is short-lived, with the 16th seed back in contention at 30-30... rollercoaster-like screams as Federer sprints to the net... Cilic can pass him, but he doesn't - his looping backhand bounces beyond the baseline. Break point Federer! The spectators raise their voices. Cheers as Cilic nets his first serve nets. Oh, come on. Federer with a backhand down the line. Break point gobbled up!

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Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

"Game on. I don't think Roger cares how he wins this year's US Open - he just wants to win it."

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Can Federer come back from two sets down? Singer Gwen Stefani probably has no doubts... A fresh shirt for the second seed, but the same turquoise and blue colours. Two quick-fire aces and the comeback is off to a fine start. Cilic with a sloppy return, the Croat then a little too cute at the net and the five-time champion holds to love.

Whoops and whistles as the players prepare for what could be the final battle of the second set. Cilic begins with an ace down the middle. 15-0. The power of Cilic's groundstrokes forcing Federer further and further back. The Swiss nets once, he nets twice. 40-0. Cheers as Cilic dumps a forehand into the tape, which sounds rather unsporting. He concludes the set with a classy ace and the 28-year-old is a set away from the US Open final. Federer must battle from two sets down if he is to win his sixth US Open title.

Jeff Tarango
Former professional tennis player on BBC Radio 5 live sports extra

"This crowd is trying to get behind Federer and turn up the pressure on Cilic."

Cilich fetches a Federer drop shot but the Croat, out of position by the net, is undone by a follow-up Federer volley. Careless at the net from Federer, allowing Cilic to come back from 40-15 to deuce, then advantage. Cilic hitting freely and without fear - a forehand to force the game back to deuce. Federer turns it on, a thumping first serve out wide followed by an angry forehand. Cilic to serve for a two-set lead.

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Heavy-duty hitting from Cilic. Gasps from a section of the spectators as he produces a colossal serve down the 'T'. Federer sticks out an arm, but he wouldn't have returned that even if he had two racquets. The Swiss nibbles at Cilic's lead, fighting to 40-30 - but Cilic can breathe easy as Federer, opening up for a forehand winner, nets.

Every Federer point greeted with raucous cheers, but Cilic still dazzling despite fighting the greatest of the greats and the crowd, too. The Croat notices Federer creeping towards the tape so he conjures a sublime lob, leaving Federer red faced and bothered. But the Swiss goes on to hold to 30, hanging on to Cilic's coattails.

Cilic the pea-shooter supreme. He throws in another ace... Federer scoots to the net, but the stooping Cilic simply passes him with a backhand winner. Cilic, indefatigable and currently indestructible.

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John McEnerney:, external "Which will be the biggest upset, Kei ousting Djokovic or if Cilic does Federer? Kei for me, Fed flat after that five-setter & there for the taking."

At 30-30, the game is in the balance but an ace to the wings swings things Federer's way. Cheers from the crowd. There's no doubting who they're supporting. If not for yourself Roger then fightback for the people... A rare successful serve and volley from Federer and the game is his.

Federer asks whether it's raining. Nice try, Rog. From 30-0 to 30-30 - Cilic straight batting a sizzling return from Federer. The crowd are vocal, cheering on their favourite Federer. The second seed exasperated as his return sails long an another ugly return means that mini revival comes to a shuddering halt.

Cilic can't move his feet quickly enough and drills a return into the tramlines, allowing Federer to wrap up a hold to 15. The Swiss far from his best, but he took a while to hit top form in the quarter-final against Gael Monfils - until the fifth set if truth be told...

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Britain's Jordanne Whiley has made history by winning the women's wheelchair doubles final.

Whiley and Japanese partner Yui Kamiji beat Dutch defending champions Jiske Griffioen and Aniek van Koot 6-4 3-6 6-3 to complete a calendar-year Grand Slam after wins in Melbourne, Paris and Wimbledon.

The win sees Whiley become the first Briton to win the same event at all four Grand Slam tournaments in the same year.

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