Roger Federer admits being wary of the threat Rafael Nadal will bring to the table when they meet for the first time in 11 years at Wimbledon on Friday.
Federer brought up a century of wins at the All England Club with a four-set win against Kei Nishikori to tee-up a mouth-watering clash against his old foe Nadal.
It will be a 40th instalment of one of tennis' great rivalries and their first here since the epic 2008 final which was famously won in five thrilling sets by the Spaniard.
But Federer is looking forward to ending the wait for a rematch on grass having already been outplayed by Nadal on clay in the French Open semi-finals last month.
"He has improved so much over the years on this surface," Federer said. "He's playing also very different than he used to.
"We haven't played each other in a long, long time on this surface. He's serving way different.
"I remember back in the day how he used to serve, and now how much bigger he's serving, how much faster he finishes points.
"It's impressive to see how sort of healthy he's stayed. A lot of them are saying, 'Oh, it's the end', by 2008. Similar to me in 2009. We're still here. So it's nice to play each other again."
Nadal brushed aside Sam Querrey in a match which was not entirely straightforward, but he returned to the last four here having lost to world No 1 Novak Djokovic 12 months ago.
It seems remarkable that Nadal and Federer have not played each other on grass since their epic encounter 11 years ago, and the Spaniard said: "It's a great feeling to be back in the semi-finals, be able to be playing at this level of tennis is great news.
"Now to play against Roger always is a unique situation. I'm excited to be back on this court against him after 11 years. It means a lot for me and probably for him, too.
"I'm excited about this match, excited about this opportunity. Always I say the same: of course, the opportunities to play against each other every time are less, but we are still here."
Nadal's victory over Federer in 2008 was the third time in a row they had played each other in the final, with the Swiss winning the previous two.
Nadal went on to win a second title in 2010 while Federer became the first man to lift the trophy eight times here when he defeated Marin Cilic in 2017.
"I just expect to play against probably the best player of the history on this surface, and I know that I have to play my best if I want to have chances to try to be in that final," said Nadal.
"I know he's playing well. He feels comfortable here. And me, too. I'm playing well."