Alyson Hannigan was convinced she'd ''messed up'' her audition for 'Buffy the Vampire Slayer'.

The 45-year-old star became a household name when she portrayed Willow Rosenberg in all six seasons of the popular series, which ran from 1997 to 2003, but she didn't think she'd get the job after a disastrous chemistry read with future co-stars Sarah Michelle Gellar and Nick Brendon.

She admitted: ''I'm a terrible auditioner. I even messed up the 'Buffy' audition.

''I walked into a door. And I forgot all my lines.''

Alyson struggled with the dialogue showrunner Joss Whedon had written especially for the try-out and even though he acknowledged she'd messed up, he still knew she was right for the part.

She continued to 'People Now': ''I had done the same lines for about eight call backs and for this particular time, it was a chemistry read with me, Sarah and Nick.

''Joss wrote a new scene especially for this audition and it was all this computer stuff - my character was very computer savvy - and it was all this computer jargon.

''We got to that part and the words just all started swimming, and I don't think I was speaking English

''And then finally I was just like, I'm just gonna stop talking now'.

''Joss later told me that 'you couldn't say the words to save your life, but I knew right then and there, because the chemistry was right there.' ''

And Alyson remembered Sarah - who played Buffy - gave her a look of pity that said, ''Oh this poor girl'', and both her and Nick were looking at her ''like, 'What did you just do?' ''