I'm sure Jannik feels nerves and pressure, he's just very good at hiding it. He has always shown some vulnerability in matches where he's pushed physically, but it must be a bit concerning for his team that he's experiencing these struggles so early in matches at the moment. In both the match against Andrey and the one against Daniil, he had quite a big physical drop off between the first and the second set. Because he's so good, he was able to win anyway, but I do wonder how he will fare in 4-5 set matches in Paris.
I would love Casper to win today, but I do feel he's just a relatively comfortable match up for Jannik, more so than Daniil is. He has never beaten Jannik. It's the Norwegian national day though, so fingers crossed for a historic victory!