US Open 2014: Simona Halep ousted by qualifier Mirjana Lucic-Baroni

Qualifier Mirjana Lucic-Baroni upset second seed Simona Halep at the US Open to reach the fourth round at a grand slam for the first time in 15 years.

The former child prodigy is now 32 but rolled back the years with a superb display of power hitting to knock out Halep 7-6 (8/6) 6-2.

A title winner at 15 and Wimbledon semi-finalist by 17, Lucic-Baroni's burgeoning career was derailed by off-court problems.

In 1998, she and her mother and siblings fled their native Croatia for the United States to escape father and coach Marinko, who she alleges physically and verbally abused her from a young age.

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Although she went on to have her great run at Wimbledon in 1999, beating Monica Seles before losing narrowly to Steffi Graf, Lucic-Baroni's success petered out.

Financial problems limited the amount she could play and she contested only two professional matches between 2004 and 2006.

But Lucic-Baroni was determined that her personal misfortune would not stop her playing tennis and in 2007 she began the long road back.

She has battled away on the lower rungs of the tennis ladder, returning to the grand-slam stage in 2010 after a gap of eight years.

Her best run until now came at Wimbledon in 2012 when she beat Marion Bartoli on her way to the third round as a qualifier.

The result will be a major disappointment for Halep, who has enjoyed an impressive season, reaching at least the quarter-finals at the other three grand slams and losing to Maria Sharapova in the French Open final.

Bizarre contest

There was also disappointment for two-time former champion Venus Williams, who served for the match against Sara Errani before losing a bizarre contest 6-0 0-6 7-6 (7/5).

Williams came into the tournament with high hopes after a good run of form and had never lost more than three games in a set against Errani before.

The American's radar was horribly off in the first set - she hit four winners and made 18 unforced errors - but she looked to have decisively turned the match in her favour in the second.

Williams served for the match at 5-3 in the decider but could not force a match point and Errani came up with two fine points to clinch the tie-break, throwing her racquet into the air and then perhaps unwisely shushing the crowd.

Bizarrely it is the second time Williams has lost a match at Flushing Meadows having lost the first set and won the second to love - she was also beaten by Kim Clijsters in 2009.

Lucic-Baroni will play Errani in the fourth round.

It was a day of shocks, and another arrived on Court 17 where 17-year-old Swiss Belinda Bencic knocked out sixth seed Angelique Kerber 6-1 7-5.

In her first visit to the last 16 at a grand slam, Bencic will play eighth seed Jelena Jankovic, who dispatched Sloane Stephens' conqueror Johanna Larsson for the loss of one game.

Peng Shuai followed up her victory over fourth seed Agnieszka Radwanska in round two by defeating 28th seed Roberta Vinci 6-4 6-3.