Juan Martin del Potro's miraculous comeback Monday against Dominic Thiem will go down as a U.S. Open classic. A clearly ill del Potro struggled during the first two sets, dropping them 6-1, 6-2. But with most of the Grandstand loudly cheering him on, del Potro improbably stormed back to win the match in five sets.
Del Potro's reward? A quarterfinal match against Roger Federer, who has stepped up his game after a shaky start to the tournament. Del Potro famously upset Federer in the 2009 U.S. Open final, but after a five-set marathon, the Argentine will need to turn in another great performance to knock out the No.