Perhaps it's the presence of Stefan Edberg in Roger Federer's camp; maybe it's the huge blister on the left hand of Rafael Nadal.
But this morning's Australian Open semi-final - to decide who plays another Swiss, Stan Wawrinka, for the title - has an extra edge to it.
This will be their 33rd meeting -Nadal leads 22-10 - but a rejuvenated Federer believes he is capable of upsetting the world No. 1 and making his first grand slam final since Wimbledon in 2012, when he beat Andy Murray to win grand slam title No. 17. He believes, but he is not so naïve to think that beating Nadal in a grand slam is not be a gargantuan task. It is one he has not managed in almost seven years and he fully expects the real Nadal, despite his nasty blister, to show up strong.
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"I don't expect the blister to be an issue," Federer said, adding that it was more likely the Spaniard would come up with "210 bombs".
"He's been tough to play against, no doubt. I'm happy I get a chance to play him in a slam again. I don't remember the last time we played."
That was here two years ago when Nadal won in four sets at the same stage, before going down in an epic, nearly six-hour battle with Novak Djokovic. With the exception of one glorious performance against Gael Monfils in round three, Nadal has not looked at his best this fortnight, but that does not mean he is going to be any easier to defeat.
The forecast is for rain here today, which means the match could well be played under the roof, which ought to favour Federer. But the Swiss said that the court-speed was not so quick to make anything easy.
"You can still play from the baseline, you can stay back, return from the back," he said. "You can do all that stuff if you want to. It's not like it's impossible. [Nadal] even does it on the indoors where you don't think that's possible. That's how he beat me in London anyway."
The London match was their most recent contest, when Nadal won their semi-final of the Barclays ATP World Tour Finals in straight sets.
Yesterday, the Spaniard was able to practise without tape on his blistered left hand but admits that the discomfort is at its worst when serving.
"The forehand is not a big issue but the serve is," he said. "I feel that with the tape I can lose the racquet when I am serving. That's a terrible feeling for a serve because then when you have this feeling you are not able to accelerate at the right moment."
When Edberg flew to Dubai before Christmas to meet with Federer to discuss a possible collaboration, the Swede expressed some ideas that could combat Nadal's strengths.
The general feeling seems to be that Edberg wants Federer to come forward more, sneaking in when he can to catch his opponent unawares.
Sweden's Jonas Bjorkman, a former world No.4 and one of the best doubles players of his generation, says Edberg is the perfect man for the job. "What Stefan was so good at and what Roger can learn from, is that he was so focused on every volley, his feet were going like this [making small steps] and he made sure he was not making errors," he said.
"Roger's got great technique but he's sometimes a little casual in his volley. And also, to move in after the shot. He hasn't done that because he didn't really need it before. But to do that I think he needs to be a little faster coming in behind his shots so he can be inside the service line to hit that first volley, because if he's too far back, Rafa is going to eat him up."
When Nadal and Federer walk on to court, Wawrinka will have his feet up, with a bowl of popcorn and, quite probably, a well-earned beer or two.
Two months short of his 29th birthday, Wawrinka's 6-3, 6-7, 7-6, 7-6 win over Tomas Berdych yesterday put him into his first grand slam final and he intends to enjoy the effort, before focusing his mind on his opponent.
"It's amazing, I didn't expect to make a final in grand slam in my career," Wawrinka said. "Tonight it's happening, so I'm really happy.
"Last year I had the feeling that I was playing better, but I was dealing better with the pressure also. I'm more mature. I'm 28 now. I've been on the tour for 10 years. Now I feel that it's my time to play my best tennis."
Wawrinka, whose one-handed backhand has been a thing of beauty all fortnight, joked that he would like it if both Nadal and Federer pulled out, to hand him the title.
"My record against Rafa is not really good, and neither against Roger," he said. "But for sure to play an all-Swiss final would be amazing, first for the country.
"Roger is the best player ever. For me it's my first final. To play against Roger would be amazing."