Longer than a marathon: Sheffield witnesses longest frame in snooker history ahead of Crucible World Championships
The Irishman beat England's David Gilbert 10-9 in the final round of qualifying at the Ponds Forge International Sports Centre in Sheffield.
The deciding frame lasted two hours, three minutes and 41 seconds - 44 seconds longer than the men's marathon record.
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Hide AdThe previous record of one hour, 40 minutes and 24 seconds was set by Alan McManus and Barry Pinches at the 2015 Ruhr Open.
O'Brien said: "Obviously in an ideal world you win a bit quicker than that.
"The balls went scrappy in the colours and I was so tired, double-checking everything and I'm so, so relieved.
"I'm looking forward to the draw now."
O'Brien,'s reward for the tiring victory was a showdown with world No 1 in the first round - after the draw was completed at 10am on Thursday morning.
The 45-year-old, who has made nine previous Crucible appearances, had not made the main draw since 2010.