Maguire's early goal handed the Lilywhites the advantage at Deepdale, while Barkhuizen struck following the break against a Bees side who lacked a cutting edge in the final third.
Brentford boss Thomas Frank named an unchanged starting team and Alex Neil made four alterations from the Preston side that drew against Nottingham Forest last time out prior to the international break.
Bryan Mbeumo wasted a great opportunity after going one-on-one but the Bees winger's heavy touch let him down as Rudd collected the loose ball.
Sergi Canos led a Brentford counter-attack after the half hour to the edge of the box but dinked a low effort well off target, before Mbeumo found the stands with a volley 10 minutes before the break.
Benrahma unleashed a fierce effort from distance three minutes before the interval which stung Rudd's hands as the hosts went into the break in front.
Mbeumo improved following the restart and curled an effort onto the roof of Rudd's net inside the opening few minutes as Brentford continued to enjoy the bulk of chances.
Preston stopper Rudd denied Watkins from an acute angle after 52 minutes following a neat exchange of possession with Benrahma, with the latter's dangerous free-kick from around 30 yards before the hour curling just wide as the Bees searched for an equaliser.
But the Lilywhites grabbed their second with 20 minutes remaining after a free Darnell Fisher on the right slid in a low cross for Barkhuizen to slot into an empty net following more questionable Brentford defending.
Barkhuizen slotted in Maguire on the break but found Jansson in the way to deny a one-on-one opportunity before the end.
The victory was Preston's third in four league games, while Brentford slip to 18th in the table after seven matches so far.