"Every victory, every set that you win, is more confidence". They met in the 2009 U.S. Open final, when del Potro won his only Grand Slam title and ended Federer's run of five championships in a row in NY.
Federer, 36, came into the year's final major with a back injury, but said his medical timeout against the German was purely a precaution.
Federer is a combined 44-0 against the first four men he's played, and he is 16-5 against del Potro.
"I knew a great new generation coming and Andrey is one of these players that have a great future and I wish him all the best", Nadal said, after clinching his spot in his 26th grand slam semi-final. "That's something that didn't happen before and is something unusual, because we played a couple of times in all the important events of the world, so will be excited and I will be very excited to play that match, of course". Federer said he was anxious about his movement in his first-round match against 19-year-old American Frances Tiafoe, then had timing issues in his second-rounder against 35-year-old Russian Mikhail Youzhny - and both of those contests went five sets. "That what's I am doing", Nadal said.
The third seed is now looking forward to a first meeting in NY against Del Potro since 2009, when the Argentinian won his only grand slam title.
"I just ran straight to the physio".
"It's a good match to look forward to".
Del Potro has gone through plenty of health problems since then, including three operations on his left wrist that forced him to miss two years' worth of Grand Slam tournaments until Wimbledon in 2016.
After two marathon five-setters to open his U.S. Open account, Federer sprinted past veteran Spaniard Feliciano Lopez in just 77 minutes in the third round and dismissed Kohlschreiber in one hour, 49 minutes without facing a break point.
When a reporter relayed to del Potro that Federer had spoken glowingly about him, del Potro responded: "Well, of course, I admire him, too".