In the first of two-play-off games for the Midlanders, they overcame the National Two West runners-up at Billesley Common.
The hosts made a fast start and led 21-0 after 25 minutes, Harry Read converting two Ben Pogson tries along with one of his own.
But Lucs got on the board before the break, George Bennett crossing the whitewash.
But a converted Elliott Creed try and Read penalty pushed Birmingham 31-5 up.
Tries from Travis Bennett-Alcock scores and Austin Nevitt, one added to by Read, effectively ended the contest.
And Nevitt then doubled his tally on the hour-mark, Read landing again for 50-5 before slotting another three points.
The visitors refused to give up, though, and Robert Aikman and George Bennett both dotted down in the final 10 minutes.
But it was Mose who had the final word, Read adding the extras to a Harry Gipson effort.
Oundle fightback sets-up Midlands derby decider
Oundle, meanwhile, secured a brilliant 29-20 victory at National Two North second-placers Tynedale.
The visitors took an early lead as Ben Young converted a Jac Arthur try.
But the Northerners replied, Cameron Grant adding to Joe Hanning’s score before landing a penalty for 10-7.
And a second Grant three-pointer gave his side a six-point lead at the break.
Anthony Maka’s converted try nudged Oundle back in front, only for the hosts to reply with one of their own from Charlie Turnbull.
But the away side came on strong in the final quarter.
First Freddie Reynolds crossed, a Young penalty making it 22-20 to Oundle.
And they teed up the Moseley decider as Young was again on target after Samson Ma’asi crossed in the final minute.
