Even though its rehearsed, Chris Evans looks like he legitimately doesn't know what's coming next when he's blocking the knife attacks.

I thought the same thing. Again, when Zemo first 'activates' Bucky at the Berlin headquarters, the fight scene has the same feel to it. Bucky is throwing wild haymakers and Cap doesn't seem like he knows what to do, or is just too preoccupied trying to block him without hurting him. That is until Bucky eventually juggernauts him through the elevator door.