Jeff Tarango
Former professional tennis player on 5 live sports extra at Flushing Meadows

Del Potro played great tennis in that set. Every forehand drove Nadal further behind the baseline and had him on the defensive.

He changed it up with some drop shots and his backhand was so consistent and so deep that the ball scooted along the court to make it really hard for Nadal to hit back hard.

Nadal needs more spin, changes of pace, scrambling and he must try to bring Del Potro into the net more, but he's so worried about the Del Potro forehand.

David Law
Radio 5 live sports extra commentator at Flushing Meadows

That game saw the best backhand that Del Potro has hit in about five years. That really pinged off the strings of his racquet like the old days.

How do you stop this guy? Nadal is way behind the baseline and looks puny in comparison.

Some might say Del Potro doesn't actually need any help the way he hammers the ball on his forehand but it can't do any harm.

Image source, Juan Martin del Potro on Twitter

It ends how you would expect a set won by Del Potro to end.

A gigantic ball-morphing forehand pops away past Rafael Nadal, making the Spaniard look like he has replaced his sneakers with concrete wellies at the back of the court.

Two sets away from a return to the final for the first time since his victory in 2009.

A mighty exchange - thunder v lightning - as Rafael Nadal and Juan Martin del Potro trade from the baseline.

Del Potro rediscovers that backhand that you thought had been amputated in one of those many bouts of surgery. A vicious deep strike that Nadal skids after in vain.

A spot of comedy to lighten the atmosphere at 30-15 as the ball-boy chases down a mighty moth and squizzes the fluttery fella flat.

Nadal into the net 40-15 and two set points.

Image source, Getty Images

David Law
Radio 5 live sports extra commentator at Flushing Meadows

That was the first truly extravagant fist pump from Nadal, he gave it the full 'Vamos!' after reaching that drop shot. He sprinted like Usain Bolt to reach the ball.

Jeff Tarango
Former professional tennis player on 5 live sports extra at Flushing Meadows

Did Nadal get a spatula out of the kitchen to scrape that ball off the ground?

What a point.

Rafael Nadal scampering, stretching and flicking magnificently to deliver a sublime soft-hand cross-court drop-shot winner.

That was 100% proof tennis.

And Rafael Nadal celebrates with an uppercut and a roar to the heavens.

That gives him the momentum to wrap up the game. Can it switch the tide in time to save this set for Rafael Nadal?

Forty-love in a twinkle as Juan Martin sends down a graphite-bending ace.

Rafael Nadal, now parked way back behind the baseline with the line judges on return, can only fend into the net.

The easiest service game so far for the man from Tandil.

Rafael Nadal is still struggling to keep a lid on the Juan Martin del Potro forehand power.

The Spaniard gets a little lucky when, forced out of court, he sees a Delpo dropper snaffled by the net at 30-15.

A roundhouse backhand from Nadal swept across court seals the game.

But Del Potro - yet to face break point - only has to hold serve twice more to take the opening set.

And he has a fresh set of fuzz to do it with...

Rafael Nadal's forehand is on a looping flightpath and kicking like a mule on impact.

Juan Martin del Potro's is flatter, harder and heavier.

It is the Argentine's style that takes the day.

Hold and high fives among the bouncing countrymen up high in the third tier.

Image source, Getty Images

Rafael Nadal has found a foxy little slice backhand approach shot that is giving Juan Martin del Potro some problems.

It is clinging to the court surface like chewing gum and Del Potro is struggling to claw it up.

The backhand is right under the microscope as Nadal trains fire on it.

Deuce.

Image source, Getty Images

Juan Martin del Potro has seen a chink in Rafael Nadal's armour to crowbar at with 0-30 on the scoreboard.

Nadal pounds away at the Argentine backhand and eventually draws the error for 15-30.

But the bazooka is still loaded.

Del Potro pummels a forehand so hard, the ball comes out in purple bruises and he has deuce.

And now break point Del Potro.

A thick net cord! Del Potro's forehand loops up, up, and...over!

Nadal is nowhere. And the first break is Delpo's!

Image source, Getty Images

I reckon the centre of Juan Martin del Potro's strings is so sweet it would fall foul of the sugar tax.

A super-charged forehand zips away to put its' owner 30-15 up.

Another bullwhip stroke off that side tracks the line perfectly for 40-30.

And a crackerjack ace out wide seals the deal.

Rafael Nadal battens down the hatches and probes the Del Potro backhand with the thoroughness of a public-school matron.

The Argentine flies long down the line and Nadal is off the hook.

Rafael Nadal suckers Juan Martin del Potro in with a dribble into the front court before passing him with an inside-out forehand with more disguise than Carlos the Jackal.

30-0. So far so good for Nadal.

But a double fault. And a forehand sprayed between the trams. The scoreline is suddenly a lot more interesting at thirty-all.

Del Potro's sledgehammer forehand sends Rafael Nadal into retreat. 30-40. Break point.

Nadal misses his first serve, has to soak up some serious forehand power, but hangs in there to make deuce.

Juan Martin del Potro runs the legs off Rafael Nadal with raking forehands and a wrong-footing backhand finishes the job for 30-0.

A gentleman with the celeste blue and white of Argentina wrapped around his head like an Elizabeth Taylor turban applauds heartily.

More encouragement for the south American contingent.

A rocket ace, Nadal dragged out of frame and off court and the game is wrapped up to love.

Image source, Getty Images

Rafael Nadal breaks out a box-fresh drop-shot, tickling a delicious forehand into the front court.

Juan Martin del Potro did not even bother getting out of the blocks for that one.

If Nadal is going to pick on Del Potro's weary legs, then the Argentine is going to play to his strengths.

A jumbo-sized forehand clatters away for 30-30. Nadal won't want to go toe-to-toe with that wing.

The Del Potro backhand is the relative runt in his arsenal and Nadal trains fire on that to seal the game.

Image source, Getty Images

Rafael Nadal to launch the first salvo of serves.

Arthur Ashe called to attention like an army regiment.

Let's go.

Juan Martin del Potro was in full rope-a-dope mode in the pre-match press conference chat.

"He's a lefty guy, so he has chance to find easily my backhand.

"So I don't know what's going to be my strategy for that match.

"But for sure I will try to make winners with my forehands and don't run too much, because my legs are tired."

The big man saved two match points earlier in his campaign as he fought off Dominic Thiem and a virus to win.

He downed Roger Federer in four last time out.

Don't underestimate Juan the man.

Image source, Getty Images