In atrocious conditions of driving rain and a strong wind, there was no shortage of excitement with the hosts twice having penalty appeals turned down by referee Andy D'Urso.
His second debatable decision appeared particularly harsh on Orient winger Moses Odubajo, who had shrugged off two tackles in the 70th minute before going to ground only to be booked for diving.
Lee Cook had also been guilty of a similar offence in the first-half.
The Robins were denied by an upright in the 67th minute after Andy Williams had latched onto a cross from Raffaele De Vita, while Alan McCormack also went close for Town when his long-range drive was turned away at full length by O's goalkeeper Jamie Jones.
At the opposite end, Town shot-stopper Wes Foderingham produced a wonderful reactionary save at point-blank range to keep out a Jimmy Smith shot with three minutes remaining.