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 6-6 Youzhny*
All very strange as Federer, pushed into the corner of the court, drifts his backhand into the net.
An ace takes him to 40-15 and then another easy shot - the sort of stroke he was nailing 10 minutes ago - clatters into the net. He'll hold, though, and we're into a tie-break.
Leon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
The backhand is where the errors are coming for Federer. That break of serve will annoy him. It will keep him out there for longer than he wants to.
Image source, Reuters*Federer 6-1 5-6 Youzhny
Hmm. The Federer backhand is getting rather acquainted with the net, and Youzhny holds.
Federer 6-1 5-5 Youzhny*
A slip in concentration from Federer as he tries to serve out the set, and it brings up two break points for Youzhny.
And Federer gives it away! A terrible forehand goes sailing way up into the stands, where a few people wisely duck out of the way. We're back on serve.
Image source, AFPLeon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
This is very chilled out from Federer.
His back problem is one of those things that could flare up at any time, he has just got to play. One movement could cause a spasm.
Image source, Reuters*Federer 6-1 5-4 Youzhny
Federer's backhand has been getting better all year, and a delicious slice down the line forces Youzhny into the splits, and he nets.
That's the only blip from the Russian though, as Federer overworks a forehand and Youzhny holds.
Federer 6-1 5-3 Youzhny*
Youzhny hasn't beaten a top 10 player at a Grand Slam since Wimbledon in 2012. There's some real glimpses of positivity, especially up at the net, but he can't string together any sustained pressure on Federer.
An ace and a delightful forehand volley are on show as Federer holds. He's a game away from taking the second set.
Image source, Rafael NadalIt's a while since he'll be in action - second match of the night session, in fact - but Rafael Nadal has already made his way to Flushing Meadows for his second-round encounter with Taro Daniel.
That hotel flooring has been polished within an inch of its life.
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*Federer 6-1 4-3 Youzhny
A hold for Youzhny, sparked by a nice run up to the net and sending over a quicker stroke that surprises Federer, who summarily nets.
Federer tries the same tactic, skipping to the net and finding the baseline yet again, and Youzhny can't pick it up in time. Deuce comes up courtesy of a double fault, but Youzhny holds his nerve and, more importantly, his serve.
Piers Newbery
BBC Sport at Flushing Meadows
Breaking (schedule) news - Kyle Edmund v Denis Shapovalov will be the second match on Arthur Ashe Stadium at about 18:00 BST on Friday.
And the night session from midnight will feature John Isner v Mischa Zverev, followed by Maria Sharapova v Sofia Kenin.
Caroline Wozniacki won't be happy....
Federer 6-1 4-2 Youzhny*
Good movement from Youzhny as he comes up to the net and smashes a backhand winner beyond Federer. Federer responds in kind, darting to the net and slicing a volley over.
0-30 soon becomes 40-30 and Federer takes a second, lining up a serve that Youzhny returns tamely. He'll hold.
Leon Smith
Great Britain Davis Cup captain on BBC Radio 5 live sports extra at Flushing Meadows
It has been a good response from Federer after that one lapse in concentration.
It was perhaps understandable because it was such one way traffic in the first set. He looks to be fully focused now.
Image source, Getty Images*Federer 6-1 3-2 Youzhny
There's a pump of the fist from Federer as a backhand volley floats onto the line, and Youzhny's return finds the very edge of the net.
That brings up two break points - and Youzhny rather hands it to his opponent with a careless forehand that goes long. Three games in a row for Fed.
Image source, ReutersFederer 6-1 2-2 Youzhny*
A tidy hold for Federer, the best of which is a forehand smash that Youzhny, lurking behind the baseline, can only watch ping past him.
We're on food watch today at the US Open...
Image source, BBC Sport*Federer 6-1 1-2 Youzhny
Now then. Federer's intensity has dipped slightly, as first a backhand and then a forehand find the net from on the baseline.
Youzhny nets to take it to 30-15, and he's instantly irked with himself as he comes forward and nets a simple return.
Both players get pushed deep behind the line but it's Federer who prevails as a return from the Russian goes long. Break point - and he takes it after a superb bit of stroke play! Federer thuds over two backhands, Youzhny meets them both, and eventually Fed hammers a forehand winner beyond him.
Federer 6-1 0-2 Youzhny*
Image source, Getty ImagesA shout of frustration from Youzhny as an attempted backhand down the line sails wide, but he pumps his fist as a Federer volley goes long.
Ooh, and now Federer's backhand goes skewhiff for 30-30, and then break point comes up as the Swiss slaps his forehand into the foot of the net.
Can Youzhny take this rare chance? He can, as Federer's loopy return goes long!
Image source, Getty Images#bbctennis
Stephanie Siu: Dimitrov OUT in three. Really wondering who I'll be seeing in the quarter-finals when I go to the US Open next week!
*Federer 6-1 0-1 Youzhny
That's much better from Youzhny - he holds straight away, courtesy of a forehand smash that Federer, legs akimbo, can't get his racquet on.
* denotes next server
Federer 6-1 Youzhny*
If you were making plans to spend the evening in front of the telly watching Federer, then I'd find something else to do. Roger appears to have plans away from the tennis court.
Image source, Reuters