Brentford's unbeaten run stretched to eight games - despite being reduced to 10 men - thanks to a Glenn Poole brace.
Midfielder Poole scored on 37 minutes before Gary Smith was sent off five minutes after the break.
Joe Devera had a chance to level but failed to convert and Poole made Barnet pay from the penalty spot with 11 minutes remaining.
Adam Birchall grabbed a consolation goal in injury time but it was not enough to rescue Barnet.
Barnet: Beckwith, Porter (Carew 75), Yakubu, Devera, Gillet, Adomah, Bishop, Wright, St Aimie (Thomas 80), Birchall, Akurang.
Subs Not Used: Harrison, Leary, Burton.
Booked: Wright, Gillet, Carew.
Goals: Birchall 90.
Brentford: Hamer, Pead (Osborne 46), Sankofa, Heywood, Dickson, Shakes, Stone, Smith, Poole, Elder (Reid 88), Connell (Milsom 65).
Subs Not Used: Simon Brown, Montague.
Sent Off: Smith (50).
Booked: Smith, Hamer, Milsom, Osborne.
Goals: Poole 36, 79 pen.
Att: 2,522
Ref: Dean Whitestone (Northamptonshire).
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