Thornensians are on their way to Twickenham after booking their place in the RFU Junior Vase final.
A 33-12 win over Mellish secured their place at the home of rugby union where they will meet Surrey side Reeds Weybridge.
Yorkshire Two side Thorne got off to a rapid start with Tom Holt crossing over after just seven minutes before converting his own score.
He then added the extras when Luke Marsden went over on the quarter hour.
By the 35 minute mark, Thorne had a sizeable cushion with Zak Holgate getting on the scoresheet.
Holgate put the game to bed 13 minutes into the second half with Mellish sparked into life five minutes later.
The hosts from the Midlands Division added another converted effort on 67 minutes, taking advantage after Tom Ambler was yellow carded for Thorne on the hour mark.
But Thorne put the exclamation point on the win when James Fenwick scored nine minutes from time and Holt added the conversion.