In a marathon match in York lasting nearly five hours, Selby fought back from the brink to win six frames on the bounce as his stunned opponent’s game disintegrated in the early hours of the morning.
A century in the final frame capped a grinding matchplay performance a certain Cliff Thorburn would have been proud of as the clock ticked over to 12.10am.
It all looked so far away when the match begun just after 7pm, Robertson in first with a 26 in the opener and after Selby missed his first black off its spot, the Australian knocked in a frame-winning 65.
Both players had their chances to win a scrappy second but when Robertson missed the remaining red off the rail when only needing a colour to follow, Selby looked certain to clear the remaining colours to level before missing the blue. Robertson repaid the compliment with an even easier miss on the same colour but knocked in the pink he required after another Selby error.
Robertson got the better of a long third littered with missed pots and solid safety play to pull three clear and piled more misery on Selby with a 105 to make it 4-0 at the interval.
Selby kept his slim hopes alive with a break of 58 to get on the scoreboard by winning the first frame after the interval before an extraordinary finish to the sixth frame saw first Selby fluff his positional shot off the final red then Robertson snooker himself from yellow to green. A protracted safety exchange followed before Robertson missed his pot on the blue, allowing Selby to pull another back.
As in the previous frame, Robertson looked well set amongst the balls before a horrendous kick on the white saw the cue ball jump in the air before leaving him out of position on the black. And a further bad contact on the brown on his next visit saw Selby take full advantage to cut the lead to just one.
Robertson was in first in the next but a tough missed red with the spider let in Selby for a superb 106 to level at 4-4 and complete his long road back to parity. It proved a momentum changer. Selby edged a marathon ninth lasting almost an hour to get to within one of victory and he finished the match in style, clenching his fist in celebration after an adrenaline charged 101 break.
In the earlier finishing match, Matthew Stevens was fast out of the traps, punishing Mark Davis with two heavy breaks, an 81 sufficient to take the opener.
Two scoring visits proved sufficient for Stevens to race two clear, the Welshman knocking in a 52. But Davis, who edged John Higgins in a final frame thriller, again proved what a good match player he can be by knocking in a vital 101 break to peg one back.
Davis was also in first in the next and looked to be on course to repeat the back-to-back centuries he made against Higgins before running out of position on 35. But a further safety error from Stevens allowed him to draw level with his second visit to the table.
A rejuvenated Davis took his first chance after the interval, knocking in a composed 80 to lead for the first time. Stevens arrested the Davis revival with a frame-winning clearance that included two tough reds on the rail to level but Davis restored his lead with a flawless 98 after Stevens let him in.
The see-saw nature of the match continued with Stevens taking the next before a break of 70 put Davis to within one of victory. And Davis booked a semi final showdown with Selby after making fewer mistakes in a tight 10th.