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PARIS — Sara Errani of Italy is playing the tournament of her dreams.

The 25-year-old native of Bologna has surged to the semifinal of the French Open in singles and the finals in doubles.

On Friday, she will take the court in Lenglen stadium with a chance to win the French Open women’s doubles title with her best friend, Roberta Vinci.

Their opponents, whose third set was postponed by darkness on Wednesday night, will be Andrea Hlavackova and Lucie Hradecka of the Czech Republic or Maria Kirilenko and Nadia Petrova of Russia.

Until this year, Errani had gained a reputation as a dogged competitor, yet one whose talents rested well outside the final rounds of the four major international championships.

But Errani began a striking surge in January. She and her longtime doubles partner, Vinci of Palermo, nearly won the Australian Open doubles title, losing in three sets to Svetlana Kuznetsova and Vera Zvonareva of Russia.

Then she and Vinci won five doubles titles around the world, at Monterrey and Acapulco, Mexico; Barcelona and Madrid, Spain; Last month, they won the Italian Open doubles title at Rome.

Three factors seem to have turned around Errani’s performances.

First, she switched to a longer racket, longer by one inch, giving her better reach and more power.

“I either got a longer arm or a longer racket,” Errani said.

Errani paid more than $30,000 to buy out her contract with one racket company to change to another, according to Ubaldo Scanagatta, a veteran Italian sports journalist who operates Ubitennis.com.

It “was a big change that make me feel much better in the court,” said Errani, who stands 5 feet 5 inches tall. “Make me feel with more power and not too difference with other players on power and these things.”

A second factor was learning to relax before matches. Where once she found it nearly impossible to sleep through the night before a big match, now she sleeps longer, although still fitfully, Scanagatta said.

Third, she hired her brother, a former top soccer player, as her personal manager, increasing her level of comfort in the business side of her career, Scanagatta said.

Her success in doubles has been eclipsed by Errani’s remarkable surge as a singles player. Previously she rarely ranked higher than the top 40. She began the year ranked 45th.

This year she has won singles titles in Acapulco, Barcelona, and Budapest, driving her singles ranking up to 24th in the world.

After this week, it will rise at least as high as 14th, according to tour projections, and she will be almost certainly Italy’s new top player, ahead of Francesca Schiavone, Flavia Panetta, and Vinci.

Still, nothing in Errani’s dozen years on the tour suggested what would happen when she stepped onto the red clay of Roland Garros 11 days ago.

Seeded 21st in singles, Errani proceeded to upset two former French Open champions, Ana Ivanovic of Serbia, who won in 2008, and Svetlana Kuznetsova of Russia, who won in 2009.

On Tuesday, she defeated a rising star, 10th seeded Angelique Kerber of Germany. It was Errani’s first defeat of a top 10 player after 28 consecutive losses.

She joked that no top ten player could defeat her 29 times in a row, a remark reminiscent of a boast in 1979 by Vitas Gerulaitis, who insisted, after 16 consecutive defeats by Jimmy Connors that, “nobody beats Vitus Gerulaitis 17 times in a row.”

In the women’s semifinals on Thursday, Errani will see if she can break another streak: Five consecutive losses to Samantha Stosur of Australia, the sixth seed and victor in their last match, at the Italian Open.

“She’s amazing player,” Errani said. “She’s very strong. So I play against her in Rome last tournament and was tough match. We play also another tight match.”