Farnham, playing their first competitive match of the season, conceded a four-goal lead to Met Police ahead of Tuesday's return leg in the Southern Counties Floodlit Cup.
On the immaculate playing surface at Imber Court on Tuesday night, the Ryman League Div II side took the lead in the first minute when John Daly headed in a corner-kick.
Farnham had their share of some attractive football and should have equalised on 25 minutes. Matt Wheeler's through-ball released Alan Morgan who fired wide with only the goalkeeper to beat.
Three minutes before half-time, Jason Prins scored from close range to leave Town with an uphill task.
The Police showed their superior quality in the second half and only some fine saves by young Daniel Vasey kept them at bay.
Prins eventually sidefooted in his second goal and then completed his hat-trick to make it 4-0.
Farnham should have pulled one back from a penalty, following Wickens' foul on Graeme Miles, but skipper Lee Raby's kick was saved by McMahon.
This Saturday, Farnham travel to local rivals Ash United (ko 3 pm). Ash lost 3-2 at Chessington & Hook on Tuesday – only their second defeat of the season. Wallingford beat Raynes Park 3-1 and go seven points clear at the top of the Combined Counties League.
Farnham Reserves are home to Sandhurst on Saturday.