No signs of Monfils crumbling under pressure. He collects two set points but, oooh, he double faults. 40-30. Federer wipes his brow with the back of his hand, is the Swiss preparing to pounce? No, not really, not at all. Monfils serves out wide and Federer's response drops into the tramlines. So, there we go. Who would have predicted that?

Image source, Getty Images

Editor-in-chief of American Vogue, Anna Wintour, is a close friend of Roger Federer, but it is his opponent who is currently in vogue. Ten out of 10 for style so for Monfils, but will he fall out of fashion as quickly as a cheap lime green turtle neck? Aggressive from Federer for a comfortable hold but Monfils has a chance to serve for the set.

Jill Craybas, US former professional tennis player on BBC Radio 5 live

"Federer is doing nothing wrong, but Monfils is on fire. He's been a lot more aggressive than in his previous matches and knew he'd have to step up.

"Monfils has been super aggressive and right now he's making everything. He could easily miss those shots at any moment, he's very streaky like that.

"Roger won't get as impatient as Grigor Dimitrov did against Monfils in the previous round."

Can Monfils continue producing moments of wizardry from his red-hot racquet? At 0-30 he looks to be heading towards a familiar lull but two unreturnable big serves later and he's level at 30-30.

Federer off key in the big moments, a rash forehand gifts Monfils advantage and the Frenchman follows up with a thunderous forehand which replays show was in by 0.0000001cm. Oof, that was close but close is close enough.

Monfils again sows some seeds of doubt at 30-30 and pounces on a disguised Federer drop shot like a panther, hunting down the ball and responding with his own venom and to deuce we go. The Swiss's first serve sees off the danger and there is no more drama to see here.

Image source, Getty Images

Grigor Dimitrov and Richard Gasquet will testify that Monfils has been in inspired form at Flushing Meadows. He has a 100% record on Arthur Ashe and momentum is currently with him. Federer drags his opponent to the net with a drop shot, volleys to send him scrambling backwards and even a man of Monfils' dexterity can do little than direct a backhand into the tramlines. From 30-0 to 30-30 but Monfils consolidates his advantage, securing the hold with a cool ace - his first of the match.

Did anyone order a dose of magic and a touch of oh la la? Fabulous from Monfils - a twist of the hips, a shuffle of the feet - for a unique forehand volley from the baseline which was surely worth the admission fee alone.

The 20th seed has found his groove and his high-risk gambling is paying off as he has accumulated two break points. Federer holds firm, dragging the game to deuce and saves a third break point with a cute volley at the net.

Too much adrenaline on the Monfils forehand and Federer has advantage - but Monfils continues to swing free and loose, a looping backhand down the line bounces on the baseline. Wonderful. The Frenchman earns a fourth break point and this time, this time, he does it! Federer wide. Monfils on the march.

Image source, Reuters

Jill Craybas, US former professional tennis player on BBC Radio 5 live

"It's very gusty down on Arthur Ashe. It's such a big stadium that it tends to create a bit of a wind tunnel. That makes it difficult to play - especially on the serve.

"The two players are very different. Roger's very calm and collected on and off the court. Whereas Monfils is defintely the showman - he likes to look like he's tired sometimes, then all of a sudden he'll come back and win. There's lots of drama in his game."

Image source, EPA

There was Leonardo Di Caprio and Brad Pitt for the quarter-final between Andy Murray and Novak Djokovic and the A-listers have turned up this evening, too. Mad Men actor John Slattery among the 22,000 watching the action on Ashe, although he doesn't look too enthralled. Former Arsenal striker Thierry Henry is also in the crowd. Back to the tennis, Federer again posing questions of the Monfils serve - stealing two points but again the Frenchman just does enough to hold.

No joy for Monfils on the Federer serve, a mixture of clean-hitting winners from the Swiss and tame returns from the Frenchman. But Federer does concede his first points on his serve. A hold to 15. The second seed solid.

Who is at the other side of the net? Gael Monfils, a player who has reached the last eight without dropping a set and beaten higher seeds Grigor Dimitrov and Richard Gasquet. But it is never easy to predict how the Frenchman will perform and he's up and down in his opening service game.

Lengthier rallies on the Monfils serve and Federer nicks two easy points for a 0-30 lead but the Frenchman serves his way out of trouble and squeezes to 40-30 with a big boomer down the middle which Federer returns long. But to deuce we go - Monfils launching a forehand long. There's advantage, two break points and in between it all a strange stooping drop shot from the baseline from Monfils. But the Frenchman pulls through, Federer ballooning a forehand at advantage.

Image source, AP

Federer, sporting the Jonny Cash look, top to toe in black, kicks off proceedings. The second seed is three matches from making more history - an 18th Grand Slam title and a sixth at Flushing Meadows.

Indeed, the 33-year-old is enjoying a revival after a torrid 2013 and playing the sort of tennis John McEnroe describes as "scary". Rapid-fire serving from the Swiss, giving Monfils little chance, and it's a comfortable hold to love.

Federer and Monfils have played each other on nine previous occasions, with Federer coming out on top seven times.

2008 Roland Garros (semi-final) - Roger Federer 6-2 5-7 6-3 7-5

2009 Roland Garros (quarter-final) Roger Federer 7-6 (6) 6-2 6-4

2010 ATP World Tour Masters 1000 Paris Hard (semi-final) - Gael Monfils 7-6(7) 6-7(1) 7-6(4)

2011 Roland Garros (quarter-final) - Roger Federer 6-4 6-3 7-6(3)

2013 ATP Masters 1000 Shanghai (Round 16) - Gael Monfils 6-4 6-7(5) 6-3

2014 ATP Masters 1000 Cincinnati (Round 16) - Roger Federer 6-4 4-6 6-3

Gael Monfils is ranked 24 in the world and is aiming to become the first player ranked outside the Top 20 to reach a US Open semi-final since Mikhail Youzhny, then ranked 54 in the world, did so in 2006.

But Federer believes the Frenchman has the potential to be a top 10 player. "He's a great mover. He's got a wonderful serve, which nobody talks about because of his athletic movement, which stands out so much," said the Swiss.

"His issues have been his fitness and the setbacks he's had because of injury, then sometimes maybe not wanting to play because of reasons only he can explain."

Image source, AP

Piers Newbery
BBC Sport at Flushing Meadows

There are a few bleary eyes around after finishes of 2.26am and 1.17 am over the last two days, but the prospect of Federer v Monfils is sharpening the mind. Federer was out hitting on Ashe with his coach and two-time champion Stefan Edberg earlier, an enticing glimpse of two generations that just missed each other.

Monfils has been remarkably composed so far in New York, albeit throwing in the odd meltdown along the way. It's a cooler, breezier night, and the general feeling is that even if it's three sets, it will be three fun sets.

Hello and welcome to live text commentary to the last quarter-final match of the 2014 US Open, featuring second seed Roger Federer and 20th seed Gael Monfils. The floodlights have been switched on, the majority of fans have filtered through the turnstiles and the players have made their way onto Arthur Ashe Stadium.

It's the history man versus the unpredictable man. The artisan versus the acrobat. The man who has won it all versus the man who should have won more. I could go on until sunrise but time is of the essence - there's a tennis match to watch.

Image source, Getty Images