Former Farnham player-manager John Cassidy continues to be a thorn in the side of his old club.
The veteran defender has schemed a number of victories against Farnham and he was at it again on Saturday as Town, after their encouraging win over Sandhurst, slumped to a disappointing defeat.
A lacklustre Farnham were exposed by the hard-working visitors.
Town enjoyed plenty of possession, but lacked the guile and imagination required to unlock a resolute Westfield defence, well marshalled by the rugged Cassidy.
Westfield took the lead from their first real attack on 20 minutes. It resulted in a corner and Parsons' kick found Stuart unchallenged to send a bullet-header past debutant goalkeeper Edmonds.
Farnham had a couple of decent efforts themselves, with Alan Morgan and Kevin Annetts going close, but were fortunate not to concede a second goal on the stroke of half-time when Reid's drive came back off the crossbar.
A number of individuals impressed for Farnham in the second half, but the team effort was lacking and Westfield remained dangerous on the counter-attack.
They scored the killer second goal when Chilton held off a challenge from Decicco and lobbed Edmonds from the edge of the area.
Farnham: Edmonds, Snowdon, Slessor, Blake, Decicco, Brown, Annetts, Hooper, Miles, Morgan, Middleton (Musselwhite). Sub (not used) Whiting.
Farnham Reserves lost 3-0 at Westfield, all the goals coming in the first half.
Farnham are away to Cobham this Saturday, with the Reserves playing at home. On Tuesday, Farnham entertain Chessington United (ko 7-45 pm).