The star, who shot to fame in 2009 when she auditioned for Cowell on U.K. Tv show Britain's Got Talent, thanked her mentor for launching her career before performing an impression of his judging technique.
Speaking on stage at the Eden Court venue in Inverness she said, "If it wasn't for one man - one special man - I wouldn't be here doing what I'm doing. I'll always be grateful to him - he believed in me from the very beginning."
Then, resting her hand under her chin in the style of Cowell, she quipped, "Now Susan, you're a little tiger now aren't you? I'll tell you what, she has potential, doesn't she?"
Boyle went on to perform impressions of fellow judges Piers Morgan and Amanda Holden, much to the audience's amusement.
Following on from her first full-length concert on Tuesday, the star will perform in Aberdeen on Thursday (04Jul13) before heading to Dundee, Glasgow and Edinburgh in Scotland, as well as and Blackpool in England.