Peyton Stearns is left to rue her inconsistency as she's taken to a deciding set by Harriet Dart.

She earns a break point after nailing a pinpoint cross-court backhand pass with Harriet Dart at the net but then sends a loose forehand long. A forehand winner at deuce gives her another chance but she plants a second-serve return into the net.

British qualifier Dart eventually comes through deuce at the fourth attempt, sticking in a baseline exchange and waiting for the error to earn advantage before converting set point with a forehand winner.

She lost her opening service game of the second set but recovered with two breaks of her own to clinch it 6-3.

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Another backhand down-the-line winner rescues Aryna Sabalenka. Deuce.

Aryna Sabalenka lashes a backhand winner down the line to save the break point, but Camila Osorio beats her with a sublime cross-court forehand to earn herself another.

Aryna Sabalenka slaps her hand off her thigh as her wide forehand gifts another break point to Camila Osorio.

After slicing into the net, Aryna Sabalenka turns to power on the next point and it pays off as Camila Osorio shanks a return wide.

The Belarusian is left stranded as she makes her way to the net and she can't adjust her feet fast enough to reach a lob attempt by Osorio. 30-30.

Camila Osorio struts back to her chair to a round of applause as she dinks over the deftest of drop shots to bring up the hold.

A groan from the crowd as Camila Osorio, after challenging Aryna Sabalenka with some hefty forehand shots, slams into the net.

The world number 52 is still smiling, though, and she clenches her fist as she lands a cross-court winner to go level at 30-30.

Unforced errors off both wings for Peyton Stearns as she gives up 0-40.

The American earns a point back as Harriet Dart returns long but then slams a cross-court forehand beyond the tramlines to gift the Briton a second break of the set.

Dart will serve to take the match into a decider.

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Camila Osorio is looking more confident, but there's not much she can do to combat a cross-court forehand winner like that from Aryna Sabalanka.

The top seed double faults, pulling Osorio up to 40-30, but the Colombian can't return the next serve and we're back level.

Both players come through holds to 30 to keep the second set on serve.

Harriet Dart closes out her service game with a whipped cross-court forehand which leaves Peyton Stearns flat-footed on the baseline.

Aryna Sabalenka lets out an angry roar and throws her hands up in frustration as she allows Camila Osorio back in at 30-30.

The Belarusian glares at her team as another skewed forehand gifts her opponent the hold. That's just the second time that Osorio has held serve in this match.

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

That will be big confidence boost.

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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.

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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.

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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.