Federer had won all 10 of his previous meetings with Robredo including in straight-sets in the fourth round of the 2009 US Open, and had looked in good touch not dropping a set in his first three rounds but the Spanish veteran was on song from the outset on Monday, and won in straight-sets 7-6 (3), 6-3, 6-4.
The 31-year-old Spaniard made a stunning run at this year's French Open winning three straight five-set matches on his way to his first quarter-final since the 2009 French Open.
Now, Robredo has made it to two Grand Slam quarter finals in the same year for the first time since 2007, and just the second time in his whole career with the world No. 22 likely in the best form of his life at present.
However, the story of the day was Federer who bowed out before the quarter finals of the US Open for the first time since 2003, and the first time at any hardcourt Grand Slam since losing in the fourth round at Flushing Meadows in 2003 as well.
Since 2003, Federer has won five US Open titles, made another final, two semis and a quarter-final before this year's shock loss to Robredo.
Federer had already dropped down to No. 7 in the world leading into the US Open but the 17-time Grand Slam winner has vowed to fight on, and bounce back at 32 years of age.
""I've definitely got to go back to work and come back stronger, get rid of this loss now as quick as I can, forget about it, because that's not how I want to play from here on. I want to play better. I know I can," Federer said.
"The story of my life is that when I lose, people are shell-shocked to see me play this way. If I win, it's the best thing. I can see that. But there's no doubt about it, I'm trying hard out there trying to make it work. Sometimes it just doesn't happen.
"It has been a difficult last three months. My consistency is just not quite there yet. Maybe on a daily basis, set-by-set or point-by-point basis, maybe that's something that has been difficult for me, so maybe that was one of the reasons I lost."
Robredo is now preparing to take Federer's place in the quarter-final that was hotly anticipated at this year's US Open with Rafael Nadal.
The world No. 2 had a scare in the opening set losing it to German Philipp Kohlschreiber in a tie-break seven points to four, but Nadal bounced back from there comfortably winning the next two sets.
However, Kohlschreiber did have a golden break point opportunity that he fluffed in the third set when he missed an overhead smash. And from that point on, Kohlschreiber's head dropped and he knew he missed his only opportunity he'd get.
He was right with Nadal ending up winning 6-7 (4), 6-4, 6-3, 6-1 to move into the quarter finals of the tournament that if he wins, he will regain the world No. 1 rankling.
Spanish world No. 4 David Ferrer had a horrid time trying to shake 18th-seed Serb Janko Tipsarevic in a thrilling four-set, fourth round battle but eventually the French Open finalist prevailed 7-6 (2), 3-6, 7-5, 7-6 (3).
That will now see Ferrer take on Frenchman Richard Gasquet in the quarter finals after he needed all of five sets to overcame Canadian big-hitter Milos Raonic 6-7 (4), 7-6 (3), 2-6, 7-6 (9), 7-5 in the final singles action of Day 8.
The last of the men's fourth round matches will now take place on Tuesday starting on Arthur Ashe Stadium with word No. 1 Novak Djokovic taking on Spanish world No. 43 Marcel Granollers who has had a tremendous run into the fourth round.
The night match on Arthur Ashe will then pit the defending US Open champion Andy Murray up against Uzbekistan's Denis Istomin.
Then on Louis Armstrong Stadium Australia's Lleyton Hewitt is looking to advance to his first Grand Slam quarter final since the 2009 Wimbledon, and first at the US Open since 2006, when he takes on Russia's 21st-seed Mikhail Youzhny.
The night match at Louis Armstrong Stadium should then be a cracker featuring the ninth-seed Stanislas Wawrinka up against the fifth-seed Tomas Berdych.