They haven't had to battle all year, their roster is good enough that they've been comfortably in a playoff spot all season. We haven't really seen this team play against pressure yet this year, and they're about to have a shit ton of pressure put on them. That can make a huge difference.
This is just a false statement lol. They just won back to back games right now to maintain the lead over Tampa, had Florida/Tampa back to back prior to this.
So you haven't really watched at all this year, I don't blame you they're not your team. To break it down
1) PP has been on fire for 2-3 months. Historically bad in the playoffs so we'll see
2) Complete team buy in and commitment to a full 2-way game
3) Matthews PKing and actually being really damn good at it
4) Physicality isn't optional, everyone, including Marner, is finishing their checks
5) Goaltending has been phenomenal all year
6) Emergence of Knies as a legitimate top 6 power forward
7) Revamped blue line that is physical and sound defensively. Tanev, Carlo, McCabe (stepped up), OEL have all been really good defensively
8) Emergence of McMann as a good 2LW
9) Most importantly, they aren't just winning games. They've completely changed the way they're playing under Berube, there's a full team commitment to defence and physical play. There was a game earlier in the year where Nylander did that typical floaty shit you'd see in the past, he didn't see the ice in the entire 3rd period. Never again.
Similar roster to the past, completely different blue line, completely different team philosophy.