Michael Appleton's side could have gone ahead early on, but Roy Carroll kept Chris Maguire at bay with an excellent save.
The Magpies worked their way into the game and, near the stroke of half time, found themselves in a good position on the edge of the U’s box, but referee Carl Boyeson stood in the way of the ball, allowing the visitors to break.
At the other end Liam Sercombe burst into the box and was hauled down by Roy Carroll, prompting the ref to award Oxford a penalty, which Sercombe himself converted.
George Baldock hit the post for the visitors early in the second half, before the Magpies – who sacked previous manager Ricardo Moniz on Tuesday – drew level when Jon Stead powered in Stanley Aborah's free-kick.
Notts then sent their home faithful into a frenzy with 15 minutes left on the clock when Curtis Thompson lashed in superbly following a wonderful lay-off by Stead to edge into the lead.
Unfortunately Oxford equalised almost instantly, as Alex MacDonald slotted home from close range in after the hosts failed to deal with a corner.
Just as it seemed like the hosts would hang on to at least a point, the 90th minute saw a draw cruelly snatched away from Notts when Callum O'Dowda fired past Carroll, prompting several of the Magpie players to slump onto the ground in shock and frustration.
And just a minute later, the hosts were wounded again as their decision to commit men forward prompted the U’s to slice through their defence and score again, this time through Kemar Roofe.
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