Just before added time in the second half, substitute Imran Kayani glanced home a superb header after meeting a sumptuous Matt Lench cross deep from the right to level the scores.
Before that, on 83 minutes fellow substitute Youssef Chentouf extraordinarily brought life back into a game that was fizzling out after smashing in an audacious strike from distance.
After an even opening exchange, the visitors threatened first after a sweeping low effort from Josh Ashby was palmed to safety by Rhys Forster.
Ogo Obi went close to opening the scoring on 19 after his curling goal bound strike took the slightest deflection to divert it wide of Ben Dudzinski’s goal.
Obi’s pace was a constant issue for the Hoops backline, and after racing beyond the defence he was hauled down just outside the area in a promising position.
Despite Slough growing into the game, Oxford City provided a sucker punch courtesy of a penalty on 32 minutes.
Josh Parker converted coolly from the spot after Lee Togwell lunged in on Zac McEachran just inside the box.
The Rebels responded well and looked to get back level swiftly after the opener with Obi causing issues with his pace in behind.
Obi was found in space down the right of the box, before drilling the ball into the side netting from a narrow angle.
On 34 minutes Johnny Goddard was also denied by a stubborn Oxford defence after having his close-range effort blocked away for a corner which resulted in Elliot Benyon firing over from the penalty spot.
Slough applied late pressure as the half concluded; Johnny Goddard found Lench in space whose driven effort was also blocked by a resolute defence.
Just three minutes after the interval, City doubled the advantage after McEachran fed Alfie Potter through on goal, before calmly placing the ball into the bottom right corner.
The interval seemed to have stifled the Rebels as Oxford looked increasingly confident, McEachran again involved as he stabbed an effort which was comfortably saved by Forster.
On 63, Parker hit a tame effort straight at Forster when he managed to find plenty of space and time in the box.
Six minutes later City ought to have killed the game off after a corner from the right found its way to Lewis Miccio, whose header from a couple of yards out went over the bar.
Slough were struggling to create any openings, but Lench sliced an effort from distance well wide of the target after a short corner routine.
It was a tale of the two substitutes in the end, which helped the Rebels produce a fantastic fightback.
The Rebels will look to register their first win of 2023 when they are next in action on the road to Tonbridge Angels next Saturday.
Image: Glenn Alcock
Oxford City Lineup
Ben Dudzinski, Lewis Miccio, Josh Ashby, Lewis Coyle, Reece Fleet, Zac McEachran, Andre Burley, Josh Parker, Alfie Potter (Klaidi Lolos 75), Aaron William-Bushell, Canice Carroll. Unused substitutes: Joe Iaciofano, Jayden Carbon, Latrell Humphrey-Ewers, Gerald Muchechetere.