Andy Murray has been concerned about cramping during matches lately.

An epic, never-ending match against a 20-year-old is just what he needs.

Image source, Getty Images

David Law
Commentator on BBC Radio 5 Live

It must be slightly irritating for Andy Murray that he has had all these chances and is yet to break.

There is a real beef behind Andy's forehand and it really does have all the earmarks of the other times he was coached by Ivan Lendl.

This is part of the Andy Murray tactic. Make every game hard work. Huge hitting from Nava - but they keep coming back.

Nava produces a second-serve ace out wide... then loses out in a lengthy rally.

So close, yet so far. Deuce again.

Just as in the first game, Emilio Nava is having to work so hard for his hold.

He's got to advantage several times but Murray keeps on dragging him back to deuce. We've been going for 34 minutes in this match so far.

David Law
Commentator on BBC Radio 5 Live

I think there are live mics in the players boxes, and they are faded up at key points so we don't hear everything all the time, but we are getting to hear what's being said from Nava's team, as part of this on-court coaching.

I don't think we're going to hear too much from Ivan Lendl, though.

Murray has to stretch out to return the serve, then spin around faster than a Strictly contestant to get back for the next shot.

He wasn't fast enough. Break point saved.

But wait, another break point.

Emilio Nava saved three break points in the first game and he's just saved another.

The American cries out in celebration as, after initially looking under the pump from a peppering of powerful Murray shots, he hits a backhand on the angle to get back to deuce.

Emilio Nava was on court for almost four hours in the first round on Monday, but he doesn't seem too bothered by that currently. Might have something to do with being 20 years old.

The American is hitting massive forehands far beyond his world ranking of 203. He halts his charge slightly with a double fault.

On the next point, Nava brings Murray forwards with a drop shot but can't pass the Brit with his forehand and that's deuce.

The net cord tries to give Nava a helping hand and Murray sprints like it's 2012 to pick it up. The American comes forward next and sets up a smash for Murray, who flicks the ball with the back of his racquet to go 40-15 up.

One big serve, one bigger forehand and Murray gets his hold.

Jonathan Jurejko
BBC Sport at Flushing Meadows

The changeover sees loads more fans pile in, but some aren't in much of a rush to sit down.

One bloke dallies right in Murray's eyeline, forcing umpire Damien Dumusois to turn around.

The French official cups his mouth with his hands, using them as a speaker to politely tell the spectator to sit down.

There is a match going on here, mate, is the gist of it.

The number one seeds in the men's doubles - Briton Joe Salisbury and American Rajeev Ram - are safely through to the second round.

They beat Federico Coria and Cristian Rodriguez 6-4 6-4 in just over an hour on court seven.

Naomi Broady
British player on BBC Radio 5 Live

All Murray can do is put pressure on Nava's big service games - and take care of his own service games. To be honest I don't think Andy has done much wrong so far.

Nava does really well at generating pace and a lot of natural explosive power. An exciting prospect not just for men's tennis but for American tennis too.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Image source, Getty Images

After having tests in New York, Andy Murray is still unsure why he is cramping in matches after the results did not indicate a serious issue.

So if they were all clear then what does he do next to overcome these cramps?

The Scot says he will monitor his food and liquid intake close to matches, saying he might have to be a "little more precise with that stuff" in hot temperatures in New York.

"Usually I am pretty precise and good with it, but it is a fine balance to make sure you're getting the right fluids when you're on court," said the three-time major champion Murray.

"I take litre-and-a-half bottles on to the court to make sure I'm drinking enough at the appropriate times. In these conditions I always try to drink a litre and a half of my sports drink in 40 minutes.

"But if you have two games which last for 15 or 20 minutes then it is difficult to make sure you're drinking enough. If you take on too much you can feel bloated."

Jonathan Jurejko
BBC Sport at Flushing Meadows

Cramp is annoying for all of us. The excruciating discomfort making you jolt and leaving you wondering why it happens.

So imagine how frustrating it is for a professional athlete. Especially mid match.

That's the concern which Andy Murray has been having in recent weeks, having regularly suffered from cramps during the North American hard-court swing.

The Scot said he was happy to get through his first-round match, which was played in hot and humid conditions, without any issues.

Today is also expected to be testing conditions, although slightly less sticky than Monday.

"Mentally it's not easy going into a five-set match in those conditions after the way the last few weeks have been for me and I did well," he said after beating Francisco Cerundolo.

I did well physically and mentally to put that to the back of my mind and find a way to get through."

Emilio Nava looks like he's settled into his rhythm now. A couple of inaccuracies let Murray get to 40-30 on the American's serve but the former world number one never really threatened to break.

Jonathan Jurejko
BBC Sport at Flushing Meadows

Not too many fans in Ashe at the moment. There never really is early doors.

Maybe that can be a help to Nava, who is playing in the world's biggest stadium for the first time.

Less eyes, less noise, less pressure? Although it still feels cavernous from court level - and he is playing Andy Murray.

Naomi Broady
British player on BBC Radio 5 Live

Lendl wants Murray to be more aggressive on his running forehand, rather than just getting the ball back in play.

Emilio Nava initially looked like a 20-year-old who has never played on the US Open's main court before - which, in fairness, he is.

But now he looks more like a youngster desperate to add a victory against Andy Murray to his CV.

He gets to 30-30 on the former champion's serve and it takes a couple of big serves from Murray to eventually stamp out the resistance.

Naomi Broady
British player on BBC Radio 5 Live

It is important for Murray to stay really solid in the first couple of games as this is where he will get the psychological advantage.

Murray has always been one of the fittest players and if he can come out on top of these longer rallies - where do his opponents find the confidence to keep going in those rallies against him.