TWO of the world's top junior tennis players were locked in a three-set struggle at the Tarka Tennis Centre this afternoon.

And after a match that lasted well over two hours, Heather Watson bowed out of the AEGON Pro-Series Barnstaple.

Britain's US Open junior champion was beaten 2-6, 6-4, 6-2 by Kristina Mladenovic, winner of the French Open junior title.

Watson, 17, had appeared on course for a comfortable victory having cruised through the first set and broken Mladenovic's serve in the first game of the second.

The 16-year-old from France pulled herself together though and found some accuracy to match the power of her serve, forcing Watson to make the errors that cost her a place in the quarter-finals.

"In the first set I wasn't missing much, but I let her in a bit and you can't afford to do that," said Watson, who knocked out second seed Melanie South yesterday.

"There was a lack of concentration and I got a bit lethargic, I wasn't moving as much.

"Kristina was able to keep concentrating and kept fighting. She played really well, she really smacks the ball.

"I was hitting the ball well but I made too many mistakes."

Watson raced into a 4-0 lead in the first set as Mladenovic made a sluggish start.

The Guernsey girl held her next two service games to take the set.

It looked like the second would produce more of the same after Watson arced a back hand over Mladenovic and into the corner to break her in game one.

But she broke back in the fourth, held serve in the fifth and broke again in the sixth.

Watson rallied to break back with a sublime backhand drop shot that made it 4-3.

With both players mixing superb shots and sloppy errors, the next two games went with serve.

Crucially, Mladenovic then broke Watson for the third time in the set, taking the match to a decider.

Mladenovic, the world number 275, took a firm grip on it by winning the first three games.

Watson, 403 places lower as she makes her first steps on the ladder, held serve for 3-1 and then saw five chances to break go begging in a marathon fifth game.

Watson showed she wasn't finished with a winning forehand pass in the first point of the next game, but her serve wasn't threatening enough and Mladenovic went 5-1 up.

Her victory was delayed as Watson broke back but, against he Briton's serve, she earned three match points.

From the second, after Mladenovic had returned long on the first, Watson put the ball out and made her exit from the singles.

"We've played three times and she's 2-1 up now, which is disappointing," said Watson.

"She came out with some big shots today and I wasn't able to keep the ball in play."

Mladenovic, who could be a dangerous player in the closing stages will meet Sweden's Johanna Larsson in the quarter-finals tomorrow.

Larsson knocked out fifth seed Andrea Hlavackova today, 6-4, 6-4.

There were no such problems for top seed Ksenia Pervak and number three Pauline Parmentier.

France's Parmentier beat her German opponent, Stephanie Gehrlein, 6-1, 6-2.

Pervak won 6-4, 6-2 against British number five Naomi Cavaday, who ousted Laura Robson yesterday.

Watson will team up with Robson in the first round of the doubles this evening.

"I'm still feeling good and I've got some energy left," said Watson. "Hopefully me and Laura can come out with a win."

Their match against number two seeds Sarah Borwell and South will start no earlier than 5.30pm.