FA Cup: Leyton Orient 2 Gloucester 0
Irish striker David Mooney broke the deadlock with three minutes remaining before Dean Cox added a second goal less than a minute later - clinching the League One side's passage into the next round.
Russel Slade's troops will now face non-league club Alfreton in the second round, after they disposed of Wrexham 4-2.
However, it was Gloucester who settled quickest and created the first real opportunity of the match.
Lewis Hogg sent in a teasing second-minute corner but Darren Edwards' attempt on goal was cleared away from danger by former Chelsea midfielder Jimmy Smith.
The visitors slowly began to find their feet and Gloucester had goalkeeper Mike Green to thank for ensuring the scores remained level at half time.
Cox was the first Orient player to test Green four minutes before the break with a tricky shot on goal but the keeper was up to the task.
Green then denied Mooney with less than two minutes left to play in the opening half.
The League One side started to flex their muscles following the interval and were dominant for extended periods.
But it took Orient up until the 87th minute to find a way past Green when Mooney headed home.
The result was then put beyond doubt before Gloucester could regroup when Cox hit the back of the net after a momentary lapse in concentration from defender Matt Coupe.