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Novak Djokovic believes beating Roger Federer is as tough a task as it has ever been as the rivals prepare for another grand slam showdown at the Australian Open.
Djokovic and Federer will face off for the 45th time when they clash in the semi-finals in Melbourne after both came through their last eight matches in straights sets on Tuesday. Djokovic eased past Kei Nishikori 6-3 6-2 6-4 while Federer beat Tomas Berdych 7-6 (7/4) 6-2 6-4.
The head-to-head between the pair currently lies firmly in the balance at 22 wins each but Djokovic has the edge in recent match-ups, winning their last three meetings in grand slams.
The Serbian has usurped his fiercest rival at the top of men's tennis but Federer, now 34, has enjoyed a renaissance, producing some of his best form in recent months and reaching two grand slam finals last year.
"You have to be on the top of your game because he hasn't really dropped the level at all I think in the last seven, eight years that I've been playing against him," Djokovic said.
"He's been playing always consistently well. I think his backhand is better than it was maybe five, six years ago.
"So he's playing some terrific tennis on the hard court. This is going to be a big challenge for both of us."
Federer continues to chase an 18th grand slam title, with his last having come in 2012, while Djokovic is trying to close the gap as he sits on 10.
Victory at the Australian Open would move the top seed level with Rod Laver and Bjorn Borg on 11, and Rafael Nadal is also within sight, four clear on 14.
"I've played these guys (Federer and Nadal) so many different occasions. I've battled them for the biggest titles in sport," Djokovic said.
"These two guys made me the player also I am today. I think these rivalries have allowed me to grow and to evolve and to understand what it takes to be on the level that they are on.
"They've been dominating tennis before Andy Murray and myself came along for many years. It took a while to get in the mix.
"It keeps going. Roger is playing really terrific tennis in last two years. We played two grand slam finals last year. I know very well how good he plays, especially in the later stages of a major event.
"He always makes you play your best. My best is what is going to be necessary to win against him. Hopefully I'll be able to deliver."
Djokovic came out on top when the pair played in last year's finals at Wimbledon and the US Open, and the suspicion remains that the Serbian, six years Federer's junior, holds the physical advantage over five sets.
"Yeah, maybe. The longer the match goes, maybe I have slightly bigger chance," Djokovic said.
"But I don't think there's too big of a difference physically. He's been winning quite comfortably this tournament. He's pretty fit. He moves very well.
"I don't still think it's something I can heavily rely on."
Federer has reached three grand slam finals since he lifted the Wimbledon title in 2012 but title number 18 has so far proved elusive.
"It's part of the reason why I guess I'm still playing," Federer said.
"I feel like I'm competitive at the top, I can beat all the guys on tour. It's nice now that in the last three slams that I've been as consistent as I have been.
"I'm playing good tennis, fun tennis for me anyway. I really enjoy being able to come to the net more like back in the day so I'm very pleased.
"It would mean a lot to me, no doubt about it."