In a Rolling Stone story posted online last week, Williams said the 16-year-old girl "shouldn't have put herself in that position."
The next day, Williams apologized in a statement. She also apologised at a news conference on Sunday.
On Monday night, a day before Williams plays her first-round match at Wimbledon, she released another statement on her website, saying she also wanted to "extend an apology to the millions of sexual assault victims in America whose pain could have been compounded by my inappropriate remarks." Sexual assault, Williams wrote, "is never acceptable and never the fault of the victim."