O’Sullivan had won their previous three meetings in 2019 – including in the Players Championship and Tour Championship finals – but it is Robertson who will face either Mark Allen or Judd Trump in Sunday’s final.
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A 66 helped O’Sullivan take the opening frame, but after he inadvertently potted the pink it was Robertson who levelled up before moving 2-1 in front with a 62 after a safety exchange.
O’Sullivan’s 81 made it 2-2 going into the short interval, but Robertson came out firing with a 108 to regain the lead.
A fraught sixth frame saw O’Sullivan trail 55-13 before he fought back to once more level the match at 3-3.
Robertson sneaked in front once more, but a speedy 86 saw O’Sullivan tie a topsy-turvy encounter.
What essentially turned into a best-of-three showdown led to a thrilling ninth frame that went down to the final black, which was eventually potted by O’Sullivan as the five-time world champion moved within a frame of victory.
However, Robertson rallied with a stunning 135 to force a decider, which the Australian took with a clearance of 90.
Allen and Trump face off on Saturday evening, with the final taking place over two sessions on Sunday.
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