A new rivalry has grown in tennis this year between U.S. Open and Olympic champion Andy Murray, left, and childhood friend Novak Djokovic, the world No. 1. &quot;People say that Murray and Djokovic are close but I think it's rare,&quot; Tu says. &quot;The best sporting rivalries are the ones where there are these very distinct, almost opposite personalities, but they're very close in terms of their competence.&quot;
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