Cameron Brannagan's penalty just before half-time, to equalise Josh Knight's strike, was enough to give Oxford a 2-1 aggregate win to send the team to a play-off final against Bolton Wanderers at Wembley on Saturday 18th May.
United named an unchanged starting line-up for the third successive game, and with the substitutes the same as well it was a familiar look to the U’s.
Peterborough were on top in the early stages, looking for parity, and Hector Kyprianou’s far-post effort found Cumming’s midriff.
One swift break down the left through Josh Murphy gave the U’s their first threatening moment ten minutes in, with Tyler Goodrham’s shot well blocked. Murphy was then sent free by a long ball from Ciaron Brown, but his cross looking for Mark Harris was cut out for a corner.
Peterborough came as close as anyone in the 23rd minute when Knight fired in a shot from the corner of the six-yard box, bringing out a fine save from Cumming.
Most of Oxford’s forward play went through Murphy and it was his run and cross that gave Goodrham another shooting opportunity, but again the Posh defence got their blocks in.
United were dealt a blow on the half hour when Goodrham went down for a second time and had to come off, to be replaced by Marcus McGuane.
Posh were racking up the set pieces and in the 41st minute they eventually made one count. A free kick was sent to the far post where Knight was waiting to fire home to take the lead on the night and level the tie on aggregate.
United’s response was almost immediate. With the game just entering first-half stoppage time, Dale was fouled on the edge of the area. Brannagan’s free kick struck Harrison Burrows' hand in the wall, and when you get a pressure penalty in a play-off semi-final, it’s Mr Pennagan that you’d want to take it. Up he stepped to blast home to restore Oxford’s one-goal advantage.
There was still time before the break for another Cumming save, this time from Joel Randall, the U’s keeper tipping his dipping shot over the bar.
For the first 20 minutes of the second half United had to weather a storm of Peterborough pressure, but weather it they did, thanks to some sterling defensive work and the occasional break away.
It was backs-to-the-wall stuff at times for the U's but the longer the game went on, the more comfortable they looked. They even carved out chances of their own, with Ruben Rodrigues finding McGuane, whose shot arrowed inches wide.
United had to regroup again when Joe Bennett limped off to be replaced by Marcus Browne, substitute Greg Leigh dropping back to his more customary full-back role.
As the game drew towards stoppage time there was more valiant defending as Long threw himself at Clarke-Harris's goalbound shot that he successfully kept out.
At times the tension was unbearable as United repelled attack after attack. Peterborough thought they had scored through Knight's diving header, but again Cumming came to Oxford's rescue, throwing himself to his right to keep the ball out. United survived wave after wave of attack but, eventually, after a lifetime, the referee blew his whistle and United were going to Wembley.
Attendance: 12,429 including 1,306 superb Oxford fans
Report: Martin Brodetsky; Photos: JasonPix, Steve Daniels, Steve Edmunds, Darrell Fisher
