Wonderful from Sloane Stephens. She rattles a rasping forehand towards the corner and Williams cannot muster the strength to respond. Two match points.

That's one point down, Williams crunching a flaky forehand into the tape from way behind the baseline. Stephens will take that.

The veteran then pushes her younger counterpart deep, poking, prodding Stephens around court before gliding towards the net to tuck away a winning volley. 30-15.

Sloane Stephens takes a mouthful of squash on board and skips towards the baseline.

She's got the momentum, can the world number 83 make it count?

Image source, Getty Images

Russell Fuller
BBC tennis correspondent at Flushing Meadows

Venus Williams is going to have to break the Sloane Stephens serve - admittedly not for the first time in this match - if she is going to take this match to a deciding tie-break.

And Stephens takes the break. She has the chance to serve for a place in the final.

Image source, Reuters

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

In the last four points I think Sloane Stephens has played the best tennis of her life.

Williams is wobbling. Stephens is sublime. She has three break points.

This is somewhere between chess and heavyweight boxing. The Americans are moving each other around the court with a superb arsenal of shots, only to find bigger, more creative strokes coming back at the them.

Stephens pulls of the deftest of lobs as Williams scrambles towards the net, and moments later she guides a drop shot almost 180 degrees across the net to leave Williams no chance. 0-30.

Russell Fuller
BBC tennis correspondent at Flushing Meadows

Boy, did Sloane Stephens deserve to keep her chances alive! That was a special game containing a special winner from Sloane Stephens.

It is not often that you look at each other in the commentary box to check that what you saw just happened.

But that was what happened after that Stephens backhand down the line.

Venus is finding her line and length right when it matters. She pins Stephens back to 30-30 with a potent forehand down the line.

Stephens clips the net with a backhand of her own, it sits up, but Williams can't punish it. She slices to the corner, Stephens looks out on her feet, but somehow she wraps a racquet around it to fling a winner down the line. 40-30. And now she holds. Wonderful fight from the 24-year-old.

Image source, Getty Images

Awkward, wayward and wide from Venus Williams as she slips into a deep Sloane Stephens forehand.

But the 37-year-old snaps a fantastic winner from a similar position moments later. 15-15.

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

Venus Williams sits there like a Egytian god with all the mascara and highlighting. She looks nerveless, but this is where it is mind over matter.

Image source, Getty Images

This set has been longer than the first two combined.

Neither player wants to let the US Open slip from their grasp just yet. Venus is poker-faced on her chair, Sloane Stephens looking just as ice cold in hers.

Who's it going to be?

Russell Fuller
BBC tennis correspondent at Flushing Meadows

There is a lot of pressure on Sloane Stephens now. The last time she came out to serve she led 4-3, not she will do so at 5-4 down.

This changeover is not going to be a comfortable 90 seconds.

Now it's Sloane Stephens' turn to go long after a bruising rally, and the 24-year-old can't hide her frustration at her choice of strokes. Williams has the chance to force Stephens to serve to stay in the match, and she does. Stephens cracks one into the net - pressure on.

Image source, Getty Images

Was that long from Venus? Sloane Stephens is going to challenge. This could be the make-or-break review. It's clipped the line from Williams! Just. She survives. Deuce.

At times, Sloane Stephens' play on the run has been quite spectacular. She gives the crowd another example of her wonderful athleticism with a passing backhand on the chase that leaves Williams desperately clambering for, but to no avail.

Williams follows up with a double fault. And then goes far too long with an edgy backhand. Break point Stephens.

Image source, Getty Images

Russell Fuller
BBC tennis correspondent at Flushing Meadows

We got what we asked for didn't we? Four games all. Will the vast experience of Venus Williams see her through here?

She takes it. Williams powers a slow second serve beyond the control of Sloane Stephens and we're all square.

Image source, Getty Images

There's a nervous quiet echoing around the Arthur Ashe Stadium right now, they've made their allegiances clear. But then the New York crowd is spoiled for choice in these women's semi-finals.

Stephens is creating problems for herself off the second serve. Williams punishes it. 30-30.

The two-time US Open champ opts for the drop shot a moment later, Stephens scuttles forward but can't pick it up. A chance for Williams to break back.

Image source, Getty Images