Fifteen-year-old Mika Stojsavljevic became the first British girl to win a junior grand slam title since 2009 as she defeated seventh seed Wakana Sonobe at the US Open.

Stojsavljevic, who hails from Acton in west London, is also the youngest junior champion at this event since 2006, when the trophy went to 15-year-old Russian prodigy Anastasia Pavlyuchenkova – later a French Open finalist.

Stojsavljevic came into this tournament as the least heralded of the three British girls in attendance, behind Orange Bowl champion Hannah Klugman and the consistent Mingge Xu. Also the youngest member of the trio, she has been training at the National Academy in Loughborough for the past three years.

National coach Katie O’Brien – a former top-100 player in the early 2010s – commended Stojsavljevic on her mental strength  after her 6-4, 6-4 victory, which meant she emulated Heather Watson’s triumph at this event in 2009. “It was exceptional how well she handled the occasion,” O’Brien said. “Her tennis level has always been there, and every match that’s gone by, she’s just grown and grown.”

Stojsavljevic’s progress in the past eight months has been striking. At January’s Australian Open junior event, you could see the outlines of a well-formed technique, especially when it comes to the silky double-hander that generates easy power on the backhand side.

At that stage, though, she wasn’t competing as effectively as she is now. During a third-round meeting with the Japanese second seed Sara Saito – who is admittedly more than two years older – she seemed to become demoralised early and sprayed unforced errors in all directions.

In New York, by contrast, Stojsavljevic has remained much more composed. She does sometimes hold her hands out towards her coaches in exasperation after a double-fault, but when her matches have become tight, she has kept flowing nicely through her strokes.

Encouragingly, Stojsavljevic is a shot-maker who doesn’t settle for simple consistency. She closed out the first set with one of her trademark shots: a clean backhand winner that crossed the court at an acute angle.

This potency had already seen her take out the No3 and No1 seeds on her way to the final, and it was too much for 16-year-old Sonobe, a left-hander who couldn’t match her for positivity as she went down by a 6-4, 6-4 scoreline.

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