Jennifer Brady continues to make the pace as he hammer down the back straight in the second set.

A jackhammer serve out wide closes the game to 15. Brady's level slipped south in the tie-break. Does she need to get the set won inside regulation if she is to extend Osaka to a third?

Image source, reuter

David Law
BBC Radio 5 Live Sports Extra tennis commentator

It's been such a clean match. Yes, there have been some errors but that's because of the incredible ferocity of the shots.

Naomi Osaka rattles though the service game to love. She now leads the ace count - seven to six.

Jennifer Brady races into a 40-0 lead, but Naomi Osaka is as tenacious as a terrier with a teddy bear.

She whittles away the next two points to crank up the pressure a couple of notches.

Brady is not to be denied though. Wherever this match goes, this is not going to be the last time that we see Brady at the business end of the big ones.

It isn't about how many points you win, it is about which ones you win. Naomi Osaka knuckles down when the pressure comes on vice-tight.

Brady is quietly, but firmly, ushered out of the game and the chance is gone for the American.

Naomi Osaka can't prise up a back-spinning backhand that torpedoes towards her shins off the Arthur Ashe surface.

The ugly end of 0-30 for the number four seed to consider.

Jennifer Brady is a tad too eager though - pumping her backhand a mite wide to alllow Osaka back to 30-30.

But this game is still in the balance as we head to deuce.

Jennifer Brady keeps on trucking. Those juggernaut groundstrokes just keep coming at autobahn speed.

A bit of Jackson Five at the changeover. That is more like it.

Image source, Reuters

Naomi Osaka's serve wobbled and offered up a break point to Jennifer Brady in the seventh game of the first set.

But it has been as imposing and smooth as the Eiger since then.

Jennifer Brady has 30-0 but gets a little too comfortable on that cushion, sinking into a backhand that slaps into the top of the net.

Better in the next rally as her angles prove too pointy and cute for Naomi Osaka. 40-15.

And the American sees it home to get herself on the board in the second.

Right, what are we eating/drinking to see us through the night? Might have a bowl of cereal soon myself. Hit us up on #bbctennis on Twitter.

Jennifer Brady is a set down for the first time in her run at the US Open...

She will serve first in the second set.

David Law
BBC Radio 5 Live Sports Extra tennis commentator

Naomi Osaka might be the fourth seed but she looks like the best player in the world at the moment.

And she only needs the one.

Naomi Osaka's quality last just a little longer, the hitting staying sparkling diamond clean as the pressure came on hard in the tie-break.

Jennifer Brady will need a fast, solid start to the second set.

Five set points for Osaka

Naomi Osaka clinically closes out two points on her own serve.

And Jennifer Brady sprays a forehand a few milimetres wide behind her own tee-off. A second mini-break down and with it all to do now...

Naomi Osaka holds the first point.

Into a rally on the second behind Brady's serve - bish-bash, wham-bam, back-forth. The longest exchange of the match and it ends with Osaka cutting off the escape routes at the net. A mini break for Osaka.

Brady stems the bleeding by winning the next point but is down a mini-break.

Image source, EPA

David Law
BBC Radio 5 Live Sports Extra tennis commentator

It feels like over the past 10 minutes that Osaka looks like the stronger of the two.

This deserves to go to the tie-break.

Naomi Osaka puts a little sauce on a cross-cout return. Jennifer Brady finds that too spicy for her taste. 30-30.

Brady lands with her first serve though in the next and is never off the front foot.

And she bags the next point as well.

Here comes the first-set shoot-out.

Naomi Osaka whacks and batters her way through a service game, shoulders loose, strokes swinging like King Louie.

Jennifer Brady has to serve to stay in it once more. She has shown no signs of doing anything but so far though.

Image source, epa

Do not pass Go, do not gather up any hopes of a break, go directly to tie-break town.

I think that is where this one is heading.

Naomi Osaka lands a dead-eyed 85mph wrong-footing winner at 40-0 down.

Brady pats her strings in appreciation and then ruthlessly takes the next point.

Naomi Osaka breezes through a service game to love to swing the spotlight back on Jennifer Brady. The underdog serves to stay in the opener next.

First though another stab of instantly forgettable dance-pop by numbers as the players sit and stew on their changeover stools.