THERE was a time, several years ago, when Roger Federer let it slip that he was not sure how much of a threat Novak Djokovic really was.

Things changed quickly as the Serb started winning grand slam titles and when the pair meet in the semi-finals of the Australian Open here tomorrow, Federer knows that he will need to play one of his best matches in years if he is to reach another grand slam final.

Tomorrow’s clash will be their 45th in all – they are level at 22-22 – so there will be no secrets between the two.

Djokovic, who yesterday beat Kei Nishikori of Japan 6-3, 6-2, 6-4, has won their past three meetings in grand slams and the last time Federer won was in the semi-finals at Wimbledon in 2012, when he went on to win the last of his 17 grand slam titles.

Federer, who beat big-serving Czech Tomas Berdych 7-6, 6-2, 6-4 yesterday, enjoys playing Djokovic because, unlike when he plays Rafael Nadal, he does not have to change his natural game.

His problem is that Djokovic has been so dominant for the past two years that it is going to take something special for Federer to turn the tables, even if he did reach the final at Wimbedon and the US Open, where the Serb stopped him.

“It would mean a lot [to win another grand slam]," Federer said. “It's part of the reason why I guess I'm still playing. 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.”

Federer’s increasing willingness to come to the net has been one of the reasons behind his consistency in the past couple of years.

Doing it regularly against Djokovic, arguably the best returner in the game and so solid from the baseline, is risky but Federer is unlikely to change his game-plan at this stage.

“Looking at the stats, it [seems like] an easy thing [to do],” Federer said. “I do feel really good at net since a few years now. It's where it all sort of started for me when I came on Tour. I know how it works up there. I still think there's room for improvement. Every player manages to defend or pass it differently.

“You would assume that these are not stats you can keep up. It's OK. As long as you're coming in on the right plays, it's OK to be beat. You just got to ask the question time and time again, in my opinion.”

That was something it took the Swiss some time to figure out but he now does it consistently and Djokovic knows that he will have to cope with an on-rushing Federer throughout the match.

“He's trying lately to come to the net more, kind of shorten up the rallies,” Djokovic said. “He definitely has the game for that. He's got a great variation from the backhand side with the slice, short slice.

“He's got great defence, amazing offence. He's very complete. He puts constant pressure on the opponent. You have to be aware at all times. You’ve got to be tough. You’ve got to be concentrated.

“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."