Everyone knows at least something about three of US Open men’s semifinalists. Roger Federer is vying for a four-peat and his 12th major title. Nikolay Davydenko has been linked to a wagering scandal. Novak Djokovic does impersonations. But what of David Ferrer, who dispatched countryman Rafael Nadal in the fourth round?

While today Ferrer is acknowledged as one of the best on clay, at 17, he was so uncommitted to the game that he would show up for practice some days and give 100 percent and some days, zero percent, according to his coach, Javier Piles. About a month after they started working together, Ferrer won a satellite tournament at home in Valencia – famous for hosting America’s Cup sailing in 2007 and 2009 – and Piles saw that Ferrer could be something special.

“The guy doesn’t want to practice, but when he fights, he wins,” Piles remembered thinking at the time.

Still, after a few months, Ferrer was ready to quit again. He said he felt guilty for his parents who were paying $4,000 a week for expenses when he wasn’t winning. He actually gave up tennis and became a construction worker – but the stint only lasted one week.

When Friday came, and it was payday, his boss handed him $30 for the week. That Monday, he called his coach and said, “Hey Javi, I go to tennis.”

Piles worked on his game and his mind – but Ferrer’s attitude didn’t change overnight. “It took two to three years,” Piles said. Several times, Ferrer would show up, hit for five minutes, then start his rant about quitting – to the point where Piles would lock him in a closet where the balls were kept for the duration of the three-hour practice, giving him only a piece of bread and a bottle of water. At noon, Piles would ask if he wanted to come out and do his conditioning. .

Still, Piles said, “We’d play challengers, and he’d want to go home again.” With Piles repeatedly coaxing him back onto the court, Ferrer broke into the Top 100 when he was 19. From then on it was easier.

Now, according to Piles, “When David is in good shape, has good mentality, it’s very easy. But I have to remind him of smaller things like how to start a match. He’s a player who wants to put 200 percent in the beginning. His serves are not one of the best. But we never talk about returning.”

Roger Federer has called Ferrer, “the best returner in the game.” When reporters told Ferrer, “Thanks Roger,” was his humble response.

Off the court, “Ferru” is an avid reader and very quiet – so quiet that a Spanish publication recently called him “Jekyll and Hyde” for the disparity between his on-court and off-court persona.

He has smashed all but three racquets he brought to North America for a month of tournaments in Montreal, Cincinnati, New Haven, and Flushing Meadows. While Federer has been taking eight to 10 racquets on court for the US Open, Ferrer has been using his last three the entire time because they’re an old Prince model that can’t be replaced in a shop.

Still, Ferrer, 25, is so generous, he comes to practice sometimes in clothing without logos because he’s given all of his good togs away to friends who want them. “He would take the smallest piece of cake,” Piles said, so his friends would have more. “If he was left with nothing, he wouldn’t care.”