"Feels great being back in the semis," the six-time Wimbledon champion said. " . . . Haven't been here in the last of couple years."
The Swiss star is two wins away from a seventh Wimbledon championship, which would equal a mark set by William Renshaw in the 1880s - back when the defending champion received a bye directly into the final - and tied by Pete Sampras in 2000.
Nothing worked for Youzhny, including a kidding plea for help from eight-time major champion Andre Agassi, who was seated next to his wife, Steffi Graf, in the front row of the Royal Box, near Prince William and his wife, Kate.
After Federer flicked one particularly impressive defensive backhand and got to break point in the third set's opening game, the Russian turned, palms up, to seek suggestions from Agassi, who smiled back. The Duke and Duchess of Cambridge applauded. Youzhny, apparently pleased to play the role of court jester, promptly double-faulted.
When a reporter made a tongue-in-cheek remark about in-match coaching being against the rules, Youzhny grinned and said, "If he helped me, I'm ready to pay a fine."
Federer will face a familiar foe Friday: No. 1 Novak Djokovic, the defending champion, who didn't have too much trouble while beating No. 31 Florian Mayer of Germany, 6-4, 6-1, 6-4, in the quarterfinals.
This will be the sixth semifinal in the last eight Grand Slam tournaments, and 27th meeting overall, for Federer and Djokovic, and their first at Wimbledon.
Federer leads 14-12, but Djokovic won six of their last seven matches, including at the French Open a month ago.
Federer, who will turn 31 on Aug. 8, has gone 21/2 years without adding to his record total of 16 Grand Slam titles. And he hasn't won Wimbledon since 2009.
If he wins Sunday's final to end his major trophy drought, he would overtake the Serb in the rankings and tie Sampras' record of 186 weeks at No. 1.
The other men's semifinal will pit No. 4 Andy Murray of Britain against No. 5 Jo-Wilfried Tsonga of France.
Neither has won a Grand Slam title or been to a Wimbledon final.
Murray is trying to become the first British man to earn the trophy at the All England Club since Fred Perry in 1936 - the last to even make it to the title match was Bunny Austin in 1938.
Murray was one point from facing a two-set deficit before coming back to eliminate No. 7 David Ferrer of Spain, 6-7 (5), 7-6 (6), 6-4, 7-6 (4), to get to the semis for the fourth year in a row. Murray lost at that stage to Andy Roddick in 2009, then to Rafael Nadal in 2010 and 2011 - and the second-seeded Nadal's stunning exit in the second round last week ratcheted up expectations that this would be Murray's year.
Tsonga got to his second consecutive Wimbledon semi by beating Philipp Kohlschreiber, 7-6 (5), 4-6, 7-6 (3), 6-2.
In the women's semifinals Thursday, 13-time Grand Slam champion Serena Williams will play No. 2-seeded Victoria Azarenka of Belarus, and No. 3 Agnieszka Radwanska of Poland will face No. 8 Angelique Kerber of Germany.
Serena Williams had to earn two doubles victories with her older sister Venus at Wimbledon on Wednesday.
The Williams sisters finally were able to complete their second-round match against Maria Kirilenko and Nadia Petrova that started Saturday but was suspended by rain. It picked up in the third set, with the Williams sisters winning, 3-6, 6-3, 9-7. They returned to the court a few hours later to beat Bethanie Mattek-Sands and Sania Mirza, 6-4, 6-3, and move into the quarterfinals.
Serena needed her left ankle retaped during that match, but her father, Richard, said it was nothing to worry about.