I have tried to picture how JA managed to inflict all those wounds without him grabbing at her. I suspect she would lunge in and stab him and then jump back out of the way like a wild animal. And when he was crawling down the hall, she was most likely jumping towards him to stab him and then would jump back to stay away from his reach.
The very 1st wound was most like a horrible wound which shocked and hurt Travis so bad that he could not fight back much. It most likely was either the slice of the throat or a stab right to his chest area.
He had no idea he was going to be attacked, so she sneakily got to within striking range and then plunged the knife deep into his chest. Or she came up behind him and was pretending to rub his back while she reached around and slit his throat.
However she did it, that very 1st wound was really bad and he then could not fight her off because he was wounded so bad.