Roger Federer V John Isner at 2007 U.S. Open Saturday

Roger Federer faces his biggest test at the 2007 U.S. Open.

And although I don't mean Roger Federer will be having a hard time beating John Isner, I do mean he'll be facing a BIG TEST on Saturday with Isner standing 6'9'' tall.

The biggest story in the 2007 U.S. Open Championships, literally, defeated Rik De Voest in the second round of the last grand slam of the tennis calendar year, setting up a third round face-off with the current king of the tennis court.

John Isner is only 22 years old and at his age, he already has some game going for him. His coach, Manuel Diaz, is rooting for his boy to win it all at the 2007 U.S. Open Championships.

''Right now he's on cloud nine. The way he's hitting his ground strokes, he's on a totally different level than he was a month ago. That's all confidence,'' Diaz said.

If there's one thing Diaz can describe John Isner, it's probably the fact that he's always eager to learn.

''One of the first things I told him was, 'You need to be a serve and volleyer,' I expected him to question it or get frustrated. But that was one thing off the bat that set him apart. He bought into it right off the bat.''

Of course, betting against Roger Federer come Saturday is still a bad idea.

Who will win the 2007 U.S. Open championships? AcesAce sportsbook has the odds.

Roger Federer EVEN -200

Rafael Nadal EVEN +350

Andy Roddick EVEN +1300

Marat Safin EVEN +4000

Want more odds? Visit OddsHQ for more tennis betting odds and the best betting lines on some of today's biggest sporting events.

2007 U.S. Open Championships Roger Federer