Scott McGleish twice fired the Chairboys into the lead, with Aaron Wilbraham equalising for Dons and O'Hanlon heading home four minutes into stoppage to share the spoils in the Buckinghamshire derby.
But Stockport's win at Peterborough means they will have to wait another day for promotion, although they are now three points clear at the top of League Two.
The Dons found it hard to break down the stubborn Wycombe defence in the first half.
They did start with intent though and on 12 minutes Keith Andrews played in Lloyd Dyer down the left and his cross was deflected back to the skipper, whose low thunderbolt was blocked just in front of the keeper by Leon Johnson.
They couldn't carry that on and the more the half went on Wycombe got into the game, playing some neat football.
And the Chairboys created a decent chance on the half-hour mark as Stefan Oakes played a magnificent ball over the defence to Gary Holt who, with the goal at his mercy, decided to lay back for McGleish instead of shoot and the danger was cleared..
Their confidence continued to grow and minutes later Oakes had a 30-yard free-kick that Willy Gueret beat out well.
Then the goal came as Russell Martin's deep corner found Johnson at the back post who nodded the ball back into the middle for McGleish, who headed home from six yards despite the efforts of Gueret and O'Hanlon on the line.
The Dons started the second half with more energy and on 55 minutes Andrews curled an effort just over from edge of box
They continued to keep the Blues penned in front of the Cowshed and the Dons created a chance when Lewington played in Dyer on goal, but his shot was from a tight angle and was just palmed out by Frank Fielding.
And then when it started to seem like it would never come, the Dons struck with a classy move on 72 minutes.
They kept the ball well before Andrews slotted in Dean Lewington down the left who squared for Wilbraham to tap in.
But with the celebrations still in full force, McGleish stunned everyone with an amazing 30-yard volley that caught Gueret off his line.
With all their hard work ruined, the home side went out for that elusive goal but again came up against a brick wall.
And the next chance fell indeed to the visitors as substitute Delroy Facey was put through on goal, but when one-on-one he shot straight at Gueret.
The home side camped outside Wycombe's goal and threw everything at the Chairboys to no avail.
And again when all hope seemed to be lost, O'Hanlon rose magnificently to head in Lewinton's corner four minutes into stoppage time.