The Thor hunk was left nursing a black eye and a nosebleed after Stewart accidentally made contact with his face during a fight scene last year (11).
Hemsworth admits he could feel the actress' knuckles getting closer and closer to him during early takes, but he was convinced that if he did get hit by the Twilight star, it wouldn't hurt that much.
In an interview on U.S. morning show Live! With Kelly on Friday (01Jun12), he said, "The scene we were shooting, she was throwing the punch, (and) each take it started getting closer and closer, and the last take I felt it kinda skim my nose. I thought, 'I should say something, but no, she's small, it won't hurt.'
"Next take - 'Bam!' My nose (was bleeding). Sharp pair of knuckles she has there, spun me over the shoulder and I didn't want any part of that fight! (There were a) couple of tears..."
Stewart recently confessed she feared she had "ruined" the movie by injuring her co-star because she was convinced they would have to abandon filming as a result of Hemsworth's injuries.