Mark Allen suffered a shock defeat by Cao Yupeng in the first round of the World Championship in Sheffield.
The world number 11 struggled throughout and was unable to get ahead at any point during the match.
It looked as though he was set to pull a frame back in the 16th, but saw the cueball roll into the pocket after potting the black to lose 10-6.
"It's very disappointing. It turns a decent season into a mediocre one," said the Northern Irishman.
"I didn't see that performance coming. I got the worse run of the ball in two sessions of snooker. It just didn't go for me. When the white went in, it summed up the match.
"I was impressed with him in the first session and I maybe underestimated him a little bit and he put me 3-0 behind. It wasn't good enough for me."
Allen looked out-of-sorts in the first session of the match, going 5-4 behind, and was fortunate not to have a deficit of more than one frame.
It was a scrappy affair with neither player able to score heavily when in amongst the balls, but the Chinese player was doing just enough to edge ahead.
And he took the opening frame of the final session, again without a score of any significance.
After his countryman Liang Wenbo's superb performance against defending champion John Higgins on the first day's play, Cao was looking to go one step further and a controlled 108 break, the first century of the match, put him three frames ahead.
Allen pulled a frame back but Cao took two more to go with one frame of victory with a tremendous 113 break.
The Northern Irishman was digging deep though, and responded with a century of his own, a 101 and the fightback was on.
Cao looked certain to win the 16th, but broke down giving Allen the chance to win the frame.
But the match ended in bizarre fashion, as Allen cleared up, only to see the cueball roll agonisingly into the corner pocket, handing Cao his victory on debut.
Earlier on in the day, 30-year-old David Gilbert caused a surprise by beating fellow Englishman Martin Gould 10-8 to win his first match at the Crucible.
Gilbert, a former potato farmer, has made only one previous appearance in the final stages which ended in a 10-7 defeat by Stephen Hendry in 2007.
"It's a massive relief to get through. To have got over the line is great, and hopefully a few of the Tamworth massive might come up and cheer for me in the next round," he said after holding off a spirited Gould fightback.