Published Wednesday, 18 January 2012
The Antrim player was beaten 6-3 by the Australian at Alexandra Palace on Tuesday evening.
Allen lost the first frame but levelled in the second with an 88.
He rode his luck in the third, winning it after getting on the first pink with a fluke en route to a break of 124 - the 134th century of his career.
The Northern Irishman looked in position to go 3-1 up but missed a long green, which allowed Robertson to equalise with a 77 clearance.
It was all square at the interval and the players continued to match each other blow for blow when play resumed, but from 3-3 Robertson stepped up a gear.
He put himself firmly in control by opening up a two-frame cushion with breaks of 100 and 71, and wrapped things up with a break of 80.
Robertson will now play Welshman Mark Williams on Friday.