Serena Williams concedes she has not been at her best at the BNP Paribas Open, despite beating Timea Bacsinszky to reach the semi-finals on Wednesday.

The American is playing at Indian Wells for the first time since ending her 14-year boycott of the event, with her father accusing fans of racial abuse amid jeers and boos following the 2001 final.

Williams defeated Bacsinszky 7-5 6-3 to book her place in the last four, where she will face Simona Halep.

"I'm just happy I was able to get through and still be alive in this tournament when I haven't clearly been the Serena that we all know," she said.

"The only thing is I know can I play a lot better. I really take a lot of solace in that.

"Even if I don't win this event, I know I can play a tremendous amount better than what I have been playing."