This isn’t Wimbledon. America’s biggest tennis event is loud, boisterous — and could throw some surprises before it ends Sept. 11. Serena Williams and Novak Djokovic are the top-ranked players in the U.S. Open, but both are struggling with injuries that could throw them off their games. Andy Murray, fresh off his Olympic triumph, could win it all — but first has to play longtime rival Lukas Rosol today. One dark horse to watch? Germany’s Angelique Kerber, who beat cramp-hobbled Slovenian Polona Hercog in her first match.