If Ivan Lendl is Andy Murray's secret weapon—the former No. 1 player turned the Scot into a Grand Slam champion—what better way to counteract that winning combination than to cozy up to Lendl's own former coach? Novak Djokovic has done just that.

Djokovic recently hired Wojtek Fibak, a former top ten player from Poland and Lendl's unofficial coach for six years in the early days of his career. "He has an important role in the team," said Djokovic of Fibak. "We know each other for many years. He's somebody that...