The U.S. Open semifinals are here, and there could be few better matchups than the Big 4 battling it out on Arthur Ashe Stadium for a shot at glory in Flushing. We'll be live blogging the first semifinal match between world No. 1 Novak Djokovic and one of history's greatest players Roger Federer. The match is sure to excite, so check back in at noon to join in on the discussion with Courtney Nguyen and the SI.com tennis team.
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