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Rafael Nadal's Grand Slam count will stay stuck at 11 for now, sidetracked by another knee problem.
The third-ranked Spaniard withdrew from the U.S. Open on Wednesday.
Tendinitis has kept him out of action since his stunning loss at Wimbledon in late June.
No problems for Novak Djokovic and Andy Murray who warmed up for the US Open in two week's time with opening round wins at the Western & Southern Open in Cincinnati.
Fresh from winning the Rogers Cup in Toronto, Djokovic beat Andreas Seppi of Italy 7-6 (4), 6-2.
Murray, the defending champion in Cincinnati, moved around the court well during his 6-2, 6-4 win over Sam Querrey.
Top seed and four-time champion Roger Federer also advanced over Alex Bogomolov
In round two action in Ladies play, Venus Williams beat South Africa's Chanelle Scheepers 2 6 6 3 6 2 .
