Federer beats Youzhny 6-1 6-7 (3-7) 4-6 6-4 6-2
Rogers and Gavrilova play longest women's match in US Open history
World number one Pliskova beats Gibbs 2-6 6-3 6-4
Seeds Dimitrov and Berdych knocked out, Del Potro through
Day four of US Open at Flushing Meadows
Federer 6-1 6-7 (3-7) 4-6 6-4 2-1 Youzhny*
This is really good from Youzhny. He's forcing Federer to run and he's missing the easy shot as yet another backhand finds a home in the net.
Oh, no! A double fault from Youzhny and you can see he's cautious about putting his weight on that leg. Deuce.
Federer 6-1 6-7 (3-7) 4-6 6-4 2-1 Youzhny*
The first advantage goes Youzhny's way but Federer saves it with a little volley.
Youzhny's striking is still crisp, though, and he gives Federer the run around before the Swiss nets. But again, Youzhny stretches to get the backhand going, and again, he nets.
Deuce number three.
Leon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
If Roger breaks in this game it will be a very quick end in this match.
Federer 6-1 6-7 (3-7) 4-6 6-4 2-1 Youzhny*
Hmm. Youzhny's serve looks to be treating him just fine. Federer first spanks a return into the net then sends a 91mph first serve wide out of play.
That's better from Federer, another smash that Youzhny works into the net, then Federer somehow saves a tussle at the net! Federer was out of that, sprawling behind the baseline as Youzhny advanced, but there was too much on the backhand. Deuce!
Federer 6-1 6-7 (3-7) 4-6 6-4 2-1 Youzhny*
Youzhny takes a long glug of water and then gets to his feet. He's walking around OK, albeit a touch gingerly, and he has a brief touch of his quad as he heads out to serve.
Leon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
It is Youzhny's left quad that cramped when he went to hit that smash. He doesn't want to do any significant damage. He is struggling to move now.
Federer 6-1 6-7 (3-7) 4-6 6-4 2-1 Youzhny*
You could see the tension in Youzhny's muscles as he jumped to meet that Federer shot.
Federer serves out quickly and Youzhny hobbles off for a sit down.
David Law
Radio 5 live sports extra commentator at Flushing Meadows
Youzhny is someone Federer has known his whole career. He won't want to see him carried off court.
Federer 6-1 6-7 (3-7) 4-6 6-4 1-1 Youzhny*
Oh! That looked so painful for Mikhail Youzhny! He leapt in the air to meet a Federer smash and, as he jumped, the cramp set in. He hobbles back to his position but he is struggling.
Image source, ReutersLeon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
Youzhny looks exhausted. The way he walked to his chair you could see he is a tired man.
I will be really surprised if Federer doesn't win from here. Roger is the champion, owns the head to head and the crowd is behind him. He is pumping his fist. He is alive. There is one winner here.
*Federer 6-1 6-7 (3-7) 4-6 6-4 1-1 Youzhny
The Arthur Ashe crowd have finally remembered that it's okay to cheer for Federer's opponent, as Mikhail Youzhny draws the forehand error out of him.
Fed gets on the board with a smash up at the net before, yet again, he sends the ball high up into the crowd. He's given them some catching practice today. Youzhny holds.
Image source, Getty ImagesLeon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
From a very bad position Roger has found a way. He was much more aggressive in the fourth set. It was more like what he was like in the first set.
He is attacking with his forehand but there is still doubt over the backhand. He is chipping it a lot more. That must be something. Whether it is pain or the confidence factor that he doesn't want to put himself under stress.
Federer 6-1 6-7 (3-7) 4-6 6-4 1-0 Youzhny*
Right then. A love hold to get things going. Pressure? What pressure? There's not a flicker on Federer's face.
*Federer 6-1 6-7 (3-7) 4-6 6-4 Youzhny
Here we go.
Federer to serve.
Federer 6-1 6-7 (3-7) 4-6 6-4 Youzhny
The last time Federer came back from a two set to one deficit to win in a best-of-five was at Wimbledon in 2016 against Cilic.
Image source, Getty Images#bbctennis
Theo Bowyer: One of the most bizarre matches I've witnessed... both players look fatigued and struggling to impose themselves.
Leon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
I think Youzhny is getting tired. We have seen him, lose his balance a couple of times in this game and that was a tired looking forehand.
Federer 6-1 6-7 (3-7) 4-6 6-4 Youzhny
We're into a decider!
Long on the forehand from Youzhny, and the Arthur Ashe Stadium gets to its feet. For the second time in three days, Roger Federer is going into a fifth set.
Image source, Getty Images*Federer 6-1 6-7 (3-7) 4-6 5-4 Youzhny
Federer picks the right time to crack his best backhand for a while, and Youzhny, slightly surprised, nets.
Set point #2.
*Federer 6-1 6-7 (3-7) 4-6 5-4 Youzhny
The crowd thought Federer had won that as a Youzhny lob looked to be drifting wide, but it was in, and Federer's return went long! Deuce!