INDIAN WELLS - Serena Williams pulled out of her Indian Wells semi-final on Friday, 14 years after her sister Venus withdrew at the same stage to spark a fan uproar that led to a Williams boycott of the event.

Serena withdrew moments before her scheduled semi-final match on Friday night with a right knee injury, ending her hopes for a storybook finish after she made the decision several months ago to finally return to the joint WTA and ATP tournament. Ironically, Venus also pulled out of her semi-final match in 2001 with a knee injury.

Serena strode out onto the court to deliver the news in person Friday to the Tennis Garden fans, who had just watched Jelena Jankovic beat Sabine Lisicki in the first women's semi-final. "A couple of days ago at my practice I injured my knee," Williams told the crowd. "Today it was a struggle to walk."

Unlike 14 years ago when she was heckled and booed in the final against Kim Clijsters, the crowd stood and applauded Serena as she spoke. There were one or two scattered boos, but they were drowned out by the loud cheering. Serena said she had an MRI scan and doctors told her she suffered a strain in her quadriceps tendon. She tried treating it with an anti-inflammation injection but it didn't feel better Serena said.

"I was just on the practice court two days ago and everything was going good," she said. "I went for a serve and just felt a super sharp pain in my knee."

Asked why she couldn't play through the pain, Serena said she didn't want to risk a long-term injury. "When you get to a level of pain where you are at nine or a 10 or even an eight, you don't want to push it because you can actually make it a lot worse," she said.

"Weighing all that together it just wasn't a good opportunity for me to play. That being said I think probably five out of 10 matches I play injured." In 2001, Venus Williams pulled out of a highly anticipated semi-final clash with her sister at the last minute with a knee injury.

Serena said Friday she didn't see the irony in it. "I don't make anything of it. I feel that was 14 years ago and this is now. I did the best I could at this event and I am really happy to have put a lot of that behind me," Serena said. The 2001 controversy began with Venus' semi-final withdrawal and then carried over into the final the next day when Serena beat Kim Clijsters to win her second Indian Wells crown.

Because most of the fans had already taken their seats for the sisters' semi-final, many reacted in anger, booing the announcement, and then Serena was heckled and booed the next day in the final. Venus, who attended the final match with her father Richard, was also jeered by fans who thought the sisters just didn't want to play each other.

Serena denied that in an interview last week, saying she "has had nothing but integrity my whole career." Serena said Friday that doctors told her she should be feeling better in a couple of days. "It's not like three or four weeks. I just really need just a couple of days and everything will settle down. "I have a tremendous amount of inflammation in my knee and it is going to go away. The most frustrating part is it is going to go away in a couple of days."

Serena said it was heartwarming to hear the cheers Friday night when she told the crowd of her decision. She said she knew this time the crowd would understand. "I didn't feel nervous about it at all," said Williams, who has received a warm welcome in the California desert this time around. "I feel like everyone is super understanding and it is a wonderful thing for me to be back here."

The injury also means Serena could miss next week's hardcourt tournament in Miami. But Serena said she would wait and see how it feels early next week. "If I am still in pain obviously I am not going to play, but I am still hopeful," she said. Serena's withdrawal means that third seed Simona Halep advanced to Sunday's final. She'll face Jankovic, who rallied to beat Lisicki 3-6, 6-3, 6-1.