Wycombe started brightly controlling possession for most of the first five minutes. The signs looked ominous for Barnet as they simply could not get near the team that pushed Chelsea so close in the League Cup semi-final.
However, Wanderers did not threaten the Barnet goal despite their obvious superiority. Instead it was the Bees who should have taken an early lead.
Jason Puncheon found Oliver Allen with a superb first-time ball and Allen fired into the top right-hand corner but was denied by a smart stop from Jamie Young. He then thwarted Adam Birchall at the near post when he pounced on the rebound.
Wycombe were not upset by their early lapse and continued to press. Sergio Raul Torres found the side netting on 17 minutes but Scott McGleish went one better on 32 minutes.
Anthony Grant who proved to be the dominant force in midfield found McGleish with a sublime through ball. The striker with time and space steadied himself in the box before calmly slotting the ball under keeper Lee Harrison.
McGleish then nearly doubled his tally in first half injury-time but this time he saw his effort bounce back off the upright after Adam Gross had been sent off moments earlier for his second-bookable offence.
In the second period Barnet played better with ten men than they did with 11, and equalised on 53 minutes. Puncheon's free-kick found Dean Sinclair in the six-yard box and he buried his header past Young.
Barnet continued to press, with Nicky Nicolau firing against the bar from 25 yards with Young well beaten. Liam Hatch was then inches from connecting with an excellent Allen cross on 68 minutes.
But Barnet deservedly grabbed all three points in the 89th minute when Vieira tapped in Sinclair's parried shot to produce the most dramatic of finales.