World No. 1 Novak Djokovic, who set up a clash with Rafael Nadal after his win over Matteo Berrettini, said he was under pressure throughout the quarter-final that he won in fourth set to enter a Grand Slam singles semi-final for the 40th time. "This match had it all: falls, crowd, break. It was a lot of intensity. I just felt under tension the entire time," Djokovic said after the end of the match. "It was just super, super stressful to constantly be under pressure on my service games, because his service games were quite smooth with the big serve. The reaction in the end was just me liberating that tension that was building up for the entire match," added the world No. 1. The Serb tennis star said he is happy with the kind of tennis he is playing. "The quality and the level of tennis that I have been playing in the last three, four weeks on clay - Rome, Belgrade and here -- is giving me good sensations and feelings ahead of that match. I am confident. I believe I can win, otherwise I would not be here. Let us have a great battle," added Djokovic and called the semi-final clash with Nadal as the biggest challenge that anyone can face on a tennis court. Nadal, who is gunning for a record 21st Grand Slam title, has won the French Open 13 times and has been in imperious form as usual on Roland Garros. "It is not like any other match. Let us face it, it is the biggest challenge that you can have: playing on clay against Nadal, on this court on which he has had so much success in his career, in the final stages of a Grand Slam. It does not get bigger than that," Djokovic said ahead of semi-final match with Nadal on Friday. "Of course, each time we face each other, there is that extra tension and expectations. [The] vibes are different walking on the court with him. But that is why our rivalry has been historic, I think, for this sport. I have been privileged to play him so many times. "[My] rivalries with him and Roger [Federer] have made me a stronger player, allowed me to understand how I need to improve my game to get to the level where they were when I started playing professional tennis. I will probably pick Rafa as the biggest rival I have ever had in my career. "The anticipation for the match against him - any match, any surface, any occasion - is always different from any other."