Leyton Orient secured promotion to League One but relegated Oxford to the Conference on a dramatic final day.
It was heartache for Oxford but joy for Orient chairman Hearn
Eric Sabin put Oxford ahead with a right-foot strike, but Orient equalised through Craig Easton's header.
The visitors took the lead when Gary Alexander chipped Billy Turley before Chris Willmott headed Oxford level.
Willmott was sent-off late on and deep in injury time Lee Steele scored the winner to seal promotion and end Oxford's 44-year League status.
It was an afternoon of high tension, with results at other grounds constantly affecting the situation.
Northampton scored a last-gasp equaliser at Grimsby, which would have been enough to score automatic promotion for Orient even if they had been held to a draw.
Oxford needed a victory to have any chance and were in with a shout until Steele's late strike sealed their fate.
Oxford manager Jim Smith hangs his head in despair
Orient attacked from the opening whistle and Turley was soon in the thick of the action, saving a left-foot Joe Keith volley.
Turley then tipped Steele's shot onto the post after the referee had played an advantage, allowing Orient to break forward.
Sabin then put Oxford in front after 14 minutes - latching on to Andrew Burgess' curling free kick and losing his marker before slotting home.
As results stood through the division at that point Oxford were out of the bottom two - but three minutes later Easton equalised.
Turley seemed to have saved Easton's header after the midfielder met Wayne Corden's cross but the referee ruled that the ball had crossed the line.
Corden, who had earlier hit the side netting, was proving to be a real menace for the Oxford defence.
He forced a save from Turley and shot wide, while Sabin was played through for Oxford but shot wide from 18 yards.
But Turley could do nothing to prevent Alexander from putting Orient ahead.
Orient led for two minutes before Willmott equalised after Glyn Garner had parried a far-post header.
The game seemed to be heading for a draw before Steele struck to ensure that Orient won automatic promotion for the first time in 36 years.
Oxford Utd: Turley, Mansell (Brooks 76), Willmott, Dempster, Robinson, Quinn, Hargreaves, Smith (Beechers 89), N'Toya, Sabin (Basham 69), Burgess.
Subs Not Used: Tardif, Sills.
Sent Off: Willmott (85).
Goals: Sabin 14, Willmott 66.
Leyton Orient: Garner, Tann, Mackie, Zakuani, Lockwood, Corden (Ibehre 82), Simpson (McMahon 87), Easton, Keith (Tudor 79), Steele, Alexander.
Subs Not Used: Morris, Barnard.
Booked: Mackie, Zakuani.
Goals: Easton 17, Alexander 64, Steele 90.
Ref: K Woolmer (Northamptonshire).