The Swiss, still seeking a record-equalling seventh title at the All England Club after losing in the quarter-finals in 2010 and 2011, produced an hour and a half of Centre Court magic to set up a last four clash with defending champion Novak Djokovic who was no less impressive in beating Florian Mayer.
With rays of sunshine finally breaking through the clouds after days of rain interruptions, two of the men's game's golden generation look to be at the peak of their powers.
In the bottom half twice champion Rafa Nadal is conspicuous by his absence after a shock second round exit but that has merely raised the stakes for Briton Andy Murray for whom opportunity has suddenly knocked.
He was in action later against Spain's less decorated Spaniard David Ferrer hoping to book a semi-final against either Jo-Wilfried Tsonga or Philipp Kohlschreiber, the second of two Germans to reach the quarter-finals.
With the Duke and Duchess of Cambridge and former Wimbledon champions Andre Agassi and Steffi Graf watching on from the Royal Box, Federer glided majestically around the turf, barely raising a sweat in a 6-1 6-2 6-2 drubbing.
Having lost all 13 of their previous meetings, Youzhny's only real hope was that the back pain that afflicted Federer in the previous round against Xavier Malisse returned.
Instead, Federer looked as smooth as ever to reach his 32nd grand slam semi-final - taking him ahead of the record he shared with American Jimmy Connors.
"I thought I played great out there today," six-times champion Federer said in a courtside interview.
"He was down in all the sets rather quickly. I am extremely happy to be back in the semi-finals here at Wimbledon."
At one stage a crestfallen Youzhny even looked up pleadingly to Agassi. "I was asking Andre for help," the Russian said.
Top seed Djokovic had a few nervous moments early on as he reacquainted himself with outdoor tennis after playing his three previous matches under Centre Court's roof.
He dropped serve in the fifth game but he soon found his range to outclass the 28-year-old Mayer.
He broke decisively in the 10th game of the first set, sprinted through the second and cruised through the third to wrap up victory in an hour and 44 minutes.
"I had a little trouble adjusting to the sun and to outdoor conditions because I played last three matches indoors. So it took me a bit of time to get into the rhythm," Djokovic told reporters.
"It was a tricky first set obviously. It was important for me to get a set lead, and after that I played much better."
Looking ahead to his 27th clash with Federer, but first on grass, Djokovic said: "This is where he won six titles. He definitely wants to prove himself and to everybody else that he can win it once again.
"We both have to play at our best in order to get a win."
