With Ryan Clarke nursing an injury, Atieno tried his luck with a 20-yard shot which the U's goalkeeper was unable to keep out despite a valiant dive.
Until that moment Oxford had recovered well from being a goal down at half-time thanks to a stirring second-half performance.
Rene Howe's 14th goal of the season gave the Gulls the lead in the 17th minute. And Martin Ling's side should have doubled their advantage in their first attack of the second half when Howe rounded Clarke only for Harry Worley to block his shot on the goalline.
Adam Chapman then scored direct from a corner to equalise for Oxford just before the hour mark. And Cristian Montano, on loan from West Ham, scored his first goal at the Kassam Stadium with a thumping header from Damian Batt's cross after 68 minutes to put the hosts in front.
Torquay's Ian Morris was shown red 11 minutes from time for a second bookable offence before Atieno snatched an unlikely point in the 90th minute.
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