Leonardo Mayer big-serves his way back to 30-30 with cannon-like tee-off.

Dan Evans nets a backhand down the line to bring up set point.

And an Evans' slice floats clear over the baseline.

Level pegs.

Image source, reu

Dan Evans runs down a mid-court bounce and flays a backhand that Leonardo Mayer can only get frame to.

Love-thirty and a glimmer. More than a glimmer.

Dan Evans serve-volleys, rushing the net and hammering away a drive-volley on the run, to take the final point.

Is Leonardo Mayer as ice-cool and red-hot on serve when the set is within sniffing distance?

We are about to find out.

Leonardo Mayer's purple patch continues.

He has landed with 17 out of 18 of his first serves in this set, and he has dropped only two points on serve.

Dan Evans puffs out his cheeks on his way to his chair. As well he might.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Evans has got to hope to get a look at a few second serves.

Mayer has served on the line or close too it a number of times and then it is difficult to get any purchase in the game.

Dan Evans keeps his cards on the table as he knuckles down and battles through a service game.

Sometimes you are cock of the walk, sometimes you are stig of the dump. 

Right now, the Briton is having to keep playing and keep believing because Mayer has the upper hand.

Russell Fuller
BBC tennis correspondent on BBC Radio 5 live sports extra

Outstanding serving from Leonardo Mayer.

Image source, Getty Images

Leonardo Mayer is yet to miss with a first serve so far in this second set. 

Twelve out of 13 and he has lost only one point against the head so far.

Imposing stuff and Dan Evans is having to batten down the hatches and hope for the storm to pass.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Mayer seems to have found his rhythm on serve.

There is a brief bit of confusion over the first point as the British barmy army band plays a few bars of a tune, Mayer asks for a pause to regain his concentration, Evans misses his signal and serves anyway.

Nothing nasty in there.

But maybe it has just lit the fuse underneath the Argentine.

He finds the centre of the strings and seizes his first break point with a lassoo forehand out wide.  

Image source, Reuters

We are still yet to have a point against serve in the second set, Leonardo Mayer holds to love. 

Great Britain's doubles player Jamie Murray, speaking courtside: "I guess Del Potro physically didn't feel good. Maybe said he has two matches in him and that was the singles against Andy and the doubles.

"I don't know if it is better for Dan or not but he has made a great start. Mayer didn't come in with confidence, he hasn't had a great year, and Dan started great. 

"He is on top of the baseline, coming forward when he gets the chance and I just hope it continues."

Image source, Getty Images

Leonardo Mayer buries a routine overhead into the net and that is the last that the Argentine sees of that game as Evans carries it off to love.

"SOO-PER SUPER DAN," chant the Great British fans.

Rebekah Humphries: YES! GET IN! Great first set Evo!

Dr Sarah Quinnell: Come on Dan. I still can't believe we are here after Friday come on GB

There is a sign bobbing around in the crowd made up of three separate letters and spelling out DAN.

Maybe I am doing down the Evans travelling fan club, but I reckon that might be a rejigged ANDY sign.

Leonardo Mayer opens up with a love service hold.

Dan Evans with a lovely forehand that tracks the sideline all the way, before he comes in and swats down the smash for 30-15.

Slick. Very slick.

A punchy serve down the middle brings up two set points and 40-15.

A repeat dose proves too much for Leonardo Mayer.

That is the set cooked. And Evans just looks like a better tennis player.

Image source, PA

Leonardo Mayer hangs tough in the set.

Argentina captain Daniel Orsanic is immediately in his man's ear at the sit-down with a theory on how the Evans tee-off can be unlocked.

Miles Maclagan
Former British Davis Cup player on Radio 5 live sports extra

Evans has got a fast arm. He will get into the high 120's mph with his serve and that is the same speed as Roger Federer serves.

It can be skiddy when it comes from a low trajectory.

Dan Evans is making this first set work for him.

A hold to love as he keeps Leonardo Mayer at a comfortable arm's length and close in on the finishline.

He looks loose and limber. Playing Stan Wawrinka in that US Open epic must have helped to stiffen the nerves for this.