It would be a birthday to remember, but the party is likely to be a quiet affair. Zheng Jie, the tiny woman from the earthquake-devastated Chinese city of Chengdu, has produced the most romantic story of Wimbledon. She arrived with Yan Zi, her doubles partner, to sharpen up before the Beijing Olympics in August and got into the singles tournament on a wild card.

But, after being knocked out of the women's doubles in the third round, the 5ft 4in Zheng suddenly finds herself thinking the unthinkable. She is the first Chinese player to reach the semi-finals of a grand-slam tournament and a win against Serena Williams today would take her to the dream of a Wimbledon final on her 25th birthday on Saturday.

Her exotic Wimbledon journey, during which she has promised her prize-money to the 70,000 victims of the earthquakes that wrecked Sichuan province in China in May, has catapulted Zheng to superstardom in her country, which seems barely to have noticed her existence before this tournament. An estimated 100 million people watched her defeat Nicole Vaidisova, of the Czech Republic, in the quarter-finals and CCTV, China's official national television station, is predicting a huge rise in viewers for her semi-final against Williams.

If the prospect of walking out on Centre Court threatens to be the most unnerving moment of Zheng's life, she does not show it. Every test so far - which has meant knocking out three seeded players, including Ana Ivanovic, the world No 1 and the top seed at Wimbledon - has been met with the same unwavering quiet calm and that is unlikely to change.

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“China has many sports in which they lead the world. Unfortunately, tennis is not one of them,” Zheng said. “I never thought I would be in the semi-final, but now I think many people will be watching in China.”

Venus Williams, the defending champion, takes on Elena Dementieva in the other semi-final and a win seems likely for a woman whose game seems to be inspired on the lawns of Wimbledon. The Russian is the highest seed, at No 5, left in the women's singles but has a reputation for wobbling as great as Venus's reputation for growing in stature as this tournament goes on.