And she gets it! A crucial break to keep Camila Osorio alive and kicking in this match.

That will be big confidence boost.

Image source, Getty Images

Camila Osorio has lost in the first round in her last three US Open appearances and it looks like she is headed for another early exit here.

Or does it?! The Colombian brings up to break back points.

Aryna Sabalenka can't convert the first break point, but she works up another one and Camila Osorio plants it into the net.

It's a long way back for the world number 59.

Dan Kiernan
Grand Slam doubles coach on BBC Radio 5 Sports Extra 2

The perfect set for Sabalenka in terms of what she could have hoped from this.

Coming in with not a lot of matches under her belt, we have talked about Osorio being the perfect opponent for her in that match, but the fact that she's come out, had to face some break points, lost a serve and had to respond - you get used to those feelings again.

It is not as clean-cut when you're not full of confidence but she is sitting down there with the first set under her belt.

Image source, Getty Images

Each miss by Aryna Sabalenka is met with a frustrated shake of the head and an unimpressed grimace, but she's sticking to Camila Osorio in the Colombian's service games and she's got herself an early chance to break here.

A double fault at 40-30 invites more pressure on Peyton Stearns' serve.

She saves three break points - ace, long return, forehand winner - before coming through deuce at the sixth attempt.

No such issues for Harriet Dart, however, who completes a brisk hold to 15 to keep her nose in front.

Aryna Sabalenka misses on the first set point, but the ball pops up nicely off the net cord on the next one and she slams the ball past Camila Osorio.

A comfortable first set for the top seed, but she still doesn't look happy.

Image source, Getty Images

Aryna Sabalenka chunters angrily to herself after slamming the ball into the net, but she follows that with an ace and then another booming serve that Camila Osorio can only sink into the net. Two set points for the Belarusian.

Camila Osorio actually throws her racquet to try and get something on that drop shot by Aryna Sabalenka, but she can't make contact.

At least the Colombian is smiling.

Camila Osorio can't catch a break from these Aryna Sabalenka forehands and the Belarusian now has two chances to restore her double break lead.

A swat of a forehand winner from Sabalenka saves the first break point, but that's an unfortunate time for the Belarusian to double fault.

That's a break rescued by Osorio, which has not improved Sabalenka's mood...

Image source, Getty Images

A shake of the head and a few muttered words from Aryna Sabalenka as two missed backhands send her 15-30 down in this latest service game.

Oh, shot! Glorious up the line winner from Camila Osoiro, who almost ends up doing the splits as she retrieves the ball, and this is a couple of break back points...

Camila Osorio fends off a break point on her way to deuce, but she can't wriggle out of the game, and that's a double-break lead for the world number one.

It's also messy from Peyton Stearns in her opening service game of the second set.

A double fault is followed by an ace before two backhand errors present Harriet Dart with two break points - can she pounce this time?

Yes, she can! On the approach, Dart places a backhand volley into a wide open court.

The British number five backs it up with a hold to 15. We're back on serve.

Image source, Getty Images

Unforced errors are flying from Harriet Dart's racquet as she's broken to 15 in the opening game of the second set.

Peyton Stearns has converted two of her six break points. Dart is 0/4.

Aryna Sabalenka finds a way through in the end to back up the break and stay in front.

Camila Osorio can't make the most of the first break point, but she stops Sabalenka from wrapping up the hold by finding the line with another brilliant winner.

The double faults are flying. This time it's Aryna Sabalenka's turn and she's not best pleased with herself.

That forehand winner down the line from Camila Osorio won't do much to improve the Belarusian's mood.

Harriet Dart saves two set points with consecutive forehand winners - the second a thunderbolt of a short cross-court return - before Peyton Stearns nets a routine forehand and smacks her racquet in frustration.

At the fourth time of asking, the American clinches the opening set 6-3.

Aryna Sabalenka won't get an easier break of serve. Five double faults in two service games for Camila Osorio and that one proves costly.

Image source, Getty Images