
Djokovic had to fight off nerves as he tried to close out an earlier win over David Ferrer, succeeding on his fifth match point after a scare from the Spaniard.
The third-seeded Serb advanced 6-0, 6-3, 7-5 to move into a match with Federer, against whom he stands 1-5 with a victory in the Montreal final of 2007.
Federer's success marked his record 15th straight trip to a Grand Slam semi-final. It also kept the Swiss safe on the number one ranking he's held for 209 weeks. Had Federer lost and Rafael Nadal somehow won the event, the Spaniard would have taken the top spot. "I heard rumours that I could lose it," Federer said of the improbable scenario. "But we're a long way away.
"I would have had to lose and he has to win. You know how tough it is to win Grand Slams," said the man who has done it a dozen times.
The Swiss master didn't have it all his way during the victory in two hours.
In each of the three sets, the top seed went up a break 2-0 over the American; in the first two sets, 12th-seed Blake broke back to temporarily force the issue.
Federer didn't make the same mistake a third time, grabbing his habitual break in the second game, but racing away didn't immediately set up victory.
Serving for it, the Swiss clipped the top of a net with a volley for a Blake break point, then sent a return surprisingly wide. Blake then held with an ace for 4-5.
A game later, Federer settled the matter with victory on his first set point.
Blake went three for three on break points while Federer moved through with 13 aces, 46 winners and five breaks of the American. It was Federer's eighth win over Blake without a loss.
Djokovic won the first seven games against the noted Spanish scrambler who lost the final last season's Masters Cup to Federer. He needed five match points to finally advance after more than two hours.
"I'm playing with a lot of emotions, good emotions, bad emotions, and I have been like that since I started playing tennis," said the third seed.
"It's really difficult sometimes to control your emotions in such big matches and important points. And it was a lot of pressure.
"But the most important thing is that I stayed focused in the match."
The Serb joined his female compatriots in the last four in Melbourne after Jelena Jankovic and Ana Ivanovic each put out a Williams sister.
Djokovic ran into trouble as he served for victory leading 5-3. Fifth seed Ferrer saved four match points in that game, putting the Serb on the back foot.
A break of Djokovic levelled the contest at five-all but Ferrer dropped the ball as he lost his own serve in the 11th game to trail 5-6.
Djokovic got a grip as he saved a break point and finally claimed a relieved victory on a fifth match point as he landed a winner.
"I surprised myself with how I played in the first two sets," said the Serb. "At the end I was very nervous, there is no excuse for that.
"I'm happy to go through. It's an amazing feeling. I'm happy that I'm playing my best tennis at the big events.,
"Hopefully this is just the start, and I can go all the way. I have to believe in myself more and more,"
Djokovic remains unbeaten on sets during the fortnight and becomes the second Serbian into the Melbourne final four after Slobodan Zivojinovic in 1985.
Federer is looking forward to facing the young Serb again, whom he beat here in the fourth round last year.
"He's done a phenomenal job getting to four Grand Slam finals at his age," said the Swiss of the 20-year-old. "He's improved a lot. But I'm always excited to be excited playing against the best in the world.
By Bill Scott, dpa