No it is not.

Two good points from John Isner.

Isner changes his shirt again. I think that one will be going straight to the bin. It's drenched.

DelPo's long limbs help him retrieve the ball. 30-30. Is this the chance?

Isner is getting annoyed at those Argentine fans I mentioned earlier. He has a word with the umpire, asking them to keep quiet between points. The Americans get behind their man. 15-15.

Isner whacks his string in frustration and then wafts his arms after missing a half-court forehand with Del Potro looking to be struggling. He dumps his next shot into the net. Three love holds in a row...

But now Isner serves up a love hold of his own. Maybe both men just want to settle this on a tie-break.

Del Potro proves that previous service game was just a blip. He wins his latest to love and Isner is the one looking much worse. He's just ambling around the baseline, going for half-volleys rather than moving his feet.

The serve is keeping him in this for now. Can that continue?

Shot! A backhand winner under serious pressure from Isner gets him to advantage.

He now pounds down what he thinks is an ace and starts to walk to his chair before hearing the dreaded words from the umpire - "let".

No bother. A brutal kicker of a serve that almost spins to Manhattan. Isner whips off his shirt at the change of ends and places the ice towel onto his shoulders.

Those Del Potro fans are on their feet now. There are about 10 or 12 of them, clapping the beat to their chant. Their man has a break point.

There'll be a 10-minute break at the end of this set due to the heat rule and both men look like they could do with it now. Del Potro stumbled in the last game but now Isner looks less than comfortable on serve.

If the rallies go on then he doesn't look like he wants to run for the ball. Deuce.

"Delllllllllll Po, Delllll Po," chant the Argentine's fans.

Del Potro pounds his way out of trouble.

Isner bends over at the back of the court with sweaty dripping off his nose. We're over the two hour mark in this match now. The conditions are testing both men.

Del Potro edges back in front but there's no stopping Isner as he wanders forward.

Deuce.

Del Potro grimaces after serving up his first double fault of the match. He's the one who needs a lift right now.

Another double fault! Two in a row from the world number three.

30-30.

The crowd is starting to get into this one now. It's not all about bashing aces at the minute. There are some decent points developing. Those supporting Isner cheer him to his seat as he holds.

That's a body blow for John Isner. He creates two opportunities but sees them disappear and then Del Potro takes the game with some excellent play as he wanders into the net.

Isner certainly doesn't have all of this American crowd on his side today. There's plenty of support for DelPo after that hold.

The second break point is saved by Del Potro. Deuce.

That's as much as I have heard the home crowd get behind the American for a while. Del Potro has to wait before serving.

Ooof. That was a chance. Isner gets into the rally but nets.

Still one more break point for Isner...

"Come on John," shout a couple of American voices in the crowd after he sees a Del Potro winner flash past him.

He responds with a forehand winner of his own. Del Potro misjudges it a little by leaving the ball before seeing it drop in.

Now DelPo goes long. 15-40. John Isner has his first break points of the match!

That's a much better service game from John Isner. He hits one wayward forehand but the rest of the points are more comfortable, helped with a good use of hawkeye.

While Isner is being made to work in his service games, Del Potro is racing through his. The third seed has a bunch of rowdy fans high in the stands and they all chant after another crunching winner that zooms through the air. DelPo levels.

But you can't do much with that. Isner reaches up and bangs a couple of serves down from the height of a window cleaner at the top of his ladder. He holds.