New York - Two triumphs from completing a calendar Grand Slam, top-ranked defending champion Serena Williams was confronted Thursday at the US Open by an opponent even she cannot defeat - rain.
US Tennis Association officials postponed the two scheduled women's semi-final matches to Friday due to forecasts of rain Thursday lasting through the night.
Top-ranked defending champion Williams now will play Italy's 43-ranked Roberta Vinci in Friday's second semi-final after Romania's second-ranked Simona Halep faces Italian 26th seed Flavia Pennetta in the opener at Arthur Ashe Stadium starting at 11 am (1500 GMT).
The winners will
Men's semi-finals on Friday were delayed two hours to 5 p.m. (2100 GMT) to allow for the extra matches.
The delays come in the final uncovered year for Arthur Ashe Stadium, which starting in 2016 will have a retractable roof to avoid any bad weather postponements.
A supporting superstructure is in place around the venue