Ronnie O'Sullivan knows exactly what Kyren Wilson did wrong before World Championship loss

Ronnie O'Sullivan has pinpointed the critical mistake he believes led to shock at the . The defending champion was expected to progress comfortably against Lei Peifan - one of the lowest-ranked players in the tournament - but fell to a narrow 10-9 defeat.

Speaking on TNT Sports afterwards, offered a little insight into why the 33-year-old came up short. He noted that Wilson didn't play poorly, he was simply outshone. "I don't think Kyren played that bad, I just think the other guy played well," The Rocket, 49, said. "Kyren just had one of those sessions tonight where nothing really went right for him. The balls were going against him, and that's just the way it can go sometimes."

O'Sullivan also praised Lei's impressive temperment and ability to thrive under pressure, something he described as a "huge asset". However, he suggested that Wilson's defeat was ultimately rooted in a misstep in his preparation for the Crucible.

"I always text Kyren through the season because I get on quite well with him," the seven-time world champion revealed. "He has gone deep in a lot of tournaments, won a lot of tournaments... [but] I think he played in too many tournaments that he didn't need to play in.

"To win this World Championship, alright you need to be playing well, but you need at some point, around February, remember that it is all about the World Championship. I saw him playing and then the next day he's in Leicester for seven or eight days. I'd be thinking I want to go and chill out and put your cue down."

He continued: "It is a very fine line but you want to come here with a spring in your step and play yourself into form, rather than being at your limit, because it probably will go the other way. I think Kyren could have missed a few tournaments because he didn't necessarily need to play then.

"This is the one you want to win, you want to come in a little undercooked. Take a month off from playing... You need to be feeling fresher for this tournament. You need to be feeling ready and strong for the quarters and the semis. To me, I think he's played too much match snooker."

Wilson's defeat saw him become the 20th victim of the 'Crucible Curse'. The curse references the fact that no first time winner has ever successfully defended their crown since the tournament moved to Sheffield in 1977.

The World No. 2 got off to a shaky start, falling 2-0 behind to Lei after the first two frames. But he fought back to put himself 6-3 up at the interval, with the second round within touching distance in the first-to-10 encounter. However, it was during the evening session that things fell apart for last year's Crucible king, as Lei won six frames in a row to go within one of victory.

Wilson almost clawed his way back after levelling the tie at nine frames apiece. But Chinese debutant Lei delivered a monumental break of 66 in the decider to . He'll face the winner of Jak Jones and Zhao Xintong - who is making his return to the Crucible after for his involvement in a betting scandal - in the next round.

O'Sullivan, meanwhile, kicks his campaign off against old rival Ali Carter on Tuesday. Victory there would set up a second round clash with either Zhang Anda or Pang Junxu. If the Wordsley native goes all the way and clinches an eighth world title, he'll become statistically the most successful player in the modern era.