Ronnie O’Sullivan branded himself “awful” despite keeping alive his hopes of a record-extending eighth UK Championship crown.
The world number one beat China’s Zhou Yuelong 6-5 in a gripping quarter-final in York.
O’Sullivan led 4-1 but slipped 5-4 down, before winning the final two frames for a fine comeback win.
“I felt a bit embarrassed at times – it was just desperation I started to play all right,” O’Sullivan told the BBC.
“I was just going through the motions and plodding away. I was just so frustrated with how poorly I played, there really was no pressure on me.
“I was awful. Technically I’m all over the gaff.”
O’Sullivan, 47, started with a superb break of 125 – the 1,267th century of his career – as he laid an early marker of intent to 25-year-old Zhou, an opponent he beat 6-0 in their previous two meetings.
A break of 68 followed as Zhou failed to pot a ball in the opening two frames, before a run of 47 saw the 39-time ranking event winner extend his lead.
O’Sullivan, appearing in his 20th UK quarter-final in 30 appearances at the tournament, used sandpaper to rectify a problem with his cue tip in the fourth frame.
His brief loss of concentration allowed Zhou to pull a frame back, but a composed 60 break looked to have put the seven-time world champion back on course for victory.
Zhou bravely rallied to win four frames in a row, but O’Sullivan made his vast experience count and held his nerve to close the match out in style with breaks of 77 and 122 to reach a 12th UK semi-final.
“Ronnie was fantastic in that last frame – that’s why he’s world number one,” said Zhou.
“He just played perfect in the last two frames, but I’m proud of the way I played.”
O’Sullivan will play Hossein Vafaei on Saturday in the first of this year’s semi-finals.
Iran’s Vafaei battled back from 4-3 down to beat China’s Zhang Anda courtesy of three century breaks.
Trump chasing world number one status
Judd Trump cruised to an impressive 6-3 victory over Mark Selby, maintaining his quest to replace O’Sullivan at the top of the world rankings.
Breaks of 100, 95, 93 and 52 did the damage as Trump ended two-time UK champion Selby’s quest for the £250,000 first prize.
And with defending champion Mark Allen and world champion Luca Brecel having already been eliminated from the tournament, Trump is the only player left this week who could be crowned the new world number one.
If he and O’Sullivan win their next matches they would meet in Sunday’s final, with the eventual winner guaranteed top position in the standings.
Trump lost the world number one mantle in August 2021 when Selby replaced him at the summit, but the following May O’Sullivan claimed it after he won a record-equalling seventh World Championship title.
“There’s a lot of pride that comes from being world number one,” said Trump, winner of three tournaments this season.
“You can play it down as much as possible, but it’s a special feeling when you can say you’re number one in what you do.”
China’s Ding Junhui, a three-time UK champion, recovered from 2-0 and 5-4 down to beat Welshman Mark Williams 6-5 and will play Trump next for a place in the final.
