Jamie McAllister celebrates with goalscorer Burton O'Brien

Aberdeen dominated for much of the Scottish Cup quarter-final replay.

But O'Brien pounced on a wayward clearance from goalkeeper David Preece to find the empty net from 35 yards and ensure a semi-final against Celtic.

The Dons then had defender Zander Diamond sent off for a second bookable offence as they suffered their first-ever defeat at the City Ground.

Livingston striker David Fernandez and equally influential defender Marvin Andrews had both been passed fit despite picking up knocks in Sunday's final victory over Hibernian.

Aberdeen made one change, former Livingston defender Michael Hart coming in for the injured Kevin McNaughton.

Hay hails "miraculous" Livi

Livingston's Roddy McKenzie was the first goalkeeper to be tested, lurching low to his right to hold a dipping drive from defender Scott Morrison.

Aberdeen were dominating possession and McKenzie had to get down swiftly to hold a drive from David Zdrilic from the edge of the area.

A tired-looking Livingston's only threat had been a speculative effort to lob Preece by Derek Lilley that drifted wide, but the goalkeeper was eventually caught out after 26 minutes.

Preece fell to the ground as he challenged Fernandez to intercept a ball to the edge of the box intended for the striker.

Zander Diamond (left) was sent off after tackling McNamee

The goalkeeper's clearance was controlled by O'Brien 35 yards out before the former Blackburn Rovers midfielder lofted the ball into the empty goal.

Drives from Morrison, Markuss Heikkinen and Diamond threatened the Livingston goal, but the home side were keeping the Dons at long range.

Livi suffered a blow on the stroke of half-time, when former Dons full-back Jamie McAllister received a booking that rules him out of the semi-final.

Aberdeen again pressed after the break and, when Diamond at last found a ball behind the Livi defence, Leigh Hinds' cross-cum-shot was cleared in the six-yard box.

Diamond was in the doghouse after 63 minutes, when he hacked down David McNamee after a penetrating run from the Livingston defender and was sent off for his second booking of the match.

Most of the match was still being played in the Livi half, but Aberdeen failed miserably to create any clear-cut chances until Paul Sheerin sent a right-foot drive a couple of feet over the bar in the dying seconds.

Livingston: McKenzie, Dorado, Andrews, Rubio, McNamee, O'Brien, Lovell, Makel, McAllister, Fernandez, Lilley.
Subs: McMenamin, Pasquinelli, McLaughlin, Brittain, Main.

Aberdeen: Preece, Hart, McGuire, Diamond, Morrison, Hinds, Sheerin, Clark, Heikkinen, Zdrilic, Muirhead.
Subs: Tiernan, Foster, Prunty, Stewart, Esson.