The ex-Chorley, Lancaster and AFC Fylde left sided player's effort proved the difference as Slyne saw off battling visitors Rochdale Sacred Heart, at Bamber Bridge's Irongate ground.
Slyne took the lead through an own goal to lead at the break before another own goal restored parity.
But Jarvis put Slyne back in control and they held on against the Manchester League side to earn their place in the final, against Fulwood Amateurs at the County Ground at Leyland.
It will be played on Tuesday March 29 with a 7.30pm kick off.
Three wise men - West Lancs :eague reps Norman Edmondson, John Brown and Andy Hosker
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