A hat-trick from Corby's Kevin Byrne helped sink St Leonards 3-1 at the Firs.
Saints badly missed the defensive qualities of injured pair Richard Callaway and Andy Johnson although boss Glyn White felt the visitors' goals all came at times when his men were in control.
Teenage goalkeeper Peter Newstead made superb early saves from Robbie Maddox and Byrne, but he was beaten on the stroke of half-time when Byrne controversially breached the offside trap to round the 17-year-old and break the deadlock.
Byrne's clever chip made it 2-0 on the hour and although debutant Peter Rhodes headed a goal back with five minutes left, the Steelmen were home and dry when Byrne completed his hat-trick in the 87th minute.
White said: "It's a disappointing start. We've got a young team and they are going to have to learn quickly that mistakes at this level will be punished."
Saints go to Tonbridge tomorrow night (7.45pm).
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