Top scorer Neal Maupay's second half penalty was enough to send Brentford into the fourth round of the FA Cup with a hard-fought 1-0 win over Oxford.
The Frenchman's sent goalkeeper Simon Eastwood the wrong way from the spot to bag his 16th goal of the season just minutes after coming off the bench and give the Championship side victory over their League One opponents.
Maupay cut in from the left wing and delayed his shot but was clipped by Curtis Nelson and referee Jeremy Simpson pointed to the spot.
The Bees created a string of chances in a one-sided first half but lacked the cutting edge to put a resilient Oxford side to the sword.
Oxford's cause was not helped when second-half substitute Shandon Baptiste fell awkwardly and was carried off on a stretcher with his leg in a brace after eight minutes of treatment.
Early on it was all Brentford, former Arsenal youngster Josh Dasilva – making his first start for the Bees – testing Eastwood with a 25-yard drive that the Oxford keeper pushed wide.
Yet it was the visitors who might have taken a shock lead in the 18th minute when James Henry's angled drive slipped through stand-in keeper Luke Daniels' fingers but rolled to safety.
The Bees should have broken the deadlock midway through the half when a slick four-man move ended with Moses Odubajo the spare man at the far post – but his first-time shot was palmed away by Eastwood.
Brentford could thank their defenders for their most potent efforts on goal before the break.
Centre-back Yoann Barbet's quick turn in the box was worthy of a forward but his finish lacked precision and Eastwood saved with his legs.
Left-back Rico Henry twice went close at the far post as first Odubajo and then Said Benrahma drilled in low crosses as Brentford patiently worked opening after opening.
But the League One side stood firm and looked to hit their hosts on the break, with Jamie Mackie asking questions of the Bees trio of centre-backs.
Ollie Watkins went close after the restart, latching onto a precise Benrahma through-ball, only to smash his shot on the run wide of the near post.
Former Brentford midfielder John Mousinho almost came back to haunt his former side with 15 minutes remaining but fired a volley well wide when well placed just 12 yards out.
That let-off saw the introduction of Maupay, who instantly gave the hosts' forward line more purpose – and his presence proved decisive moments later.
Oxford rallied after going behind and threw everything at the Bees, Marcus Browne forcing home keeper Daniels to tip his dipping effort over.
Brentford centre-back Julian Jeanvier came to his side's rescue deep into added time – but in the end Thomas Frank's side did just enough to progress.
