Djokovic has two fellow Serbians in the women's semifinals.
No. 3 Jelena Jankovic ousted defending champion Serena Williams, and No. 4 Ana Ivanovic beat Venus Williams 7-6 (3), 6-4.
It's the second time in four majors that the Serbian trio has made it to the semis, repeating their run at the last French Open, and gives the end of the women's draw a distinctly eastern European accent.
Ivanovic, who lost the French final to Justine Henin, faces Slovakia's Daniela Hantuchova, who advanced to her first Grand Slam semifinal with a 6-2, 6-2 defeat of Agnieszka Radwanska.
Jankovic takes on last year's losing finalist Maria Sharapova of Russia, who ended No. 1-ranked Henin's 32-match winning streak in the quarterfinals.
Ivanovic had never taken a set off Venus Williams in four meetings, including the semifinals at Wimbledon and the fourth round at the U.S. Open. But she was sharper from the start against Williams, who had her left thigh heavily wrapped.
''I was looking forward for some revenge,'' Ivanovic said. ''I'm just so, so happy I managed to step up.''
In the late men's doubles match, two-time defending champions and top-seeded Bob and Mike Bryan went down 6-3, 5-7, 7-6 (5) to Mahesh Bhupathi and Mark Knowles in the quarterfinals.
Federer had more to play for against Blake than just his 8-0 record against the American and his bid for a 13th major, which would move him within one of Pete Sampras' record.
One of the anomalies of the rankings is that despite his domination last season — 68-9 with a tour-high eight titles — Federer could have lost the top spot he's held since February 2004. Nadal would have taken over if he'd reached the Australian Open final and Federer lost to Blake.
''I heard rumors I could lose it,'' Federer said, mockingly. ''Someone reminded me of it.''
With a tiebreaker looming in the first set, Federer was at his usual best under pressure, breaking Blake as he served at 5-6.
Blake saved two set points at 4-5 in the second and three more after falling behind 6-2 in the tiebreaker, but Federer cashed his sixth.
He was cruising at 5-1 in the third set when Blake ran off three straight games, but Federer finally held to finish.
''I really went in thinking I had a good chance to win,'' Blake said. ''I played pretty well, but he came up with some of his best at the right times, and that was the difference.''
It was the same for Djokovic, who had set points against Federer in the U.S. Open final but could not convert them.
Against Ferrer, he was only troubled when it was time to close out, dropping his serve and losing his temper before regaining his composure.
''As the third player of the world, I have a lot of expectations and pressure, and sometimes it's difficult to stay calm on the court,'' Djokovic said. ''I'm working on that. I'm still young and I still need to improve some elements in the game as well as the mental stabilization.''
Things changed for Djokovic when he beat Federer and Nadal en route to the Montreal title in August, then reached the U.S. Open final. He is widely considered a worthy No. 3.
''They were saying the year after a breakthrough year is the most difficult one. But you know, I'm feeling really, really good,'' Djokovic said. ''I'm playing with a lot of confidence.
''Playing a semifinal in a Grand Slam has become my routine in the last year or so. But I'm always trying to push myself on the most important events to play my best tennis, which I did, and it's a positive thing for the future.''