Serena 'pain-free' for US Open, says coach

World number one Serena Williams is "pain-free" as she embarks on winning a modern era record 23rd Grand Slam title at the US Open, her coach said Sunday. The American star, who is also chasing a record seventh crown in New York, has been struggling with a right shoulder injury which contributed to an early loss at the Olympics and forced a withdrawal from last week's Cincinnati tournament. "She has been pain-free for a few days now," coach Patrick Mouratoglou told ESPN on Sunday.