LONDON - All it took was a couple of questionable calls for Novak Djokovic to snap at the chair umpire in the second game of his third-round match at Wimbledon. "As soon as you give a guy like Novak the tools to step on the gas, he will step on the gas," said Gulbis, who has been a top 10 player and a French Open semifinalist but missed chunks of time because of injuries, dropping his ranking outside the top 500.