Dunstablians found themselves overpowered in the second half at S&L Corby on Saturday and lost 34-15.
At the midway stage of this Midlands Three East (South) clash, Dees had been holding their own after S&L had moved into a 10-point lead early on through a converted try and penalty.
But then the visitors bounced back with uncoverted tries from Luke Ashton and Robert Thorne, as S&L missed two penalties to make it 10-10 at the break.
However in the second period the hosts romped into a 29-10 lead thanks to three tries, two converted.
Dunstablians replied when Campbell Haig crossed the white line after a crossfield kick from Zach Bourne, but S&L added a further converted try to wrap up a convincing victory.
This weekend Dunstablians make the short journey to Stockwood Park in the Bedfordshire Cup Final.