[...] what would Mac do now that professional tennis is using, at least in some tournaments, an instant replay system? Would he turn into a player as calm as Roger Federer?

[...] There were 229 challenges in the U.S. Open. Players were right on 72 of them. That's 31.4 percent. Benjamin Becker, the guy who ended Andre Agassi's career, challenged three calls, and was correct on all three. But this is the interesting part. Federer, the best player in the world, challenged 17 calls. He was right on seven of them. And Andy Roddick, the best player in the United States, challenged 10 calls. He was right on two of them.