Serena Williams lost her first match since telling the world she is ready to leave professional tennis. No one knows exactly how many more matches Williams will play before walking away. The 23-time Grand Slam champion exited the National Bank Open on Wednesday night with a 6-2, 6-4 loss to Belinda Bencic. The second-round match at the hard-court tune-up for the U.S. Open came a day after the 40-year-old Williams announced “the countdown has begun” on her playing career, saying she wants to have another child and pursue business interests. She made it sound as if her final goodbyes could come at the U.S. Open. It begins Aug. 29 in New York.