Ronnie O'Sullivan lets feelings known on Kyren Wilson's performance against Lei Peifan

Ronnie O'Sullivan believes a key miscalculation led to surprising at the . Wilson, last year's winner, was expected to breeze past Lei Peifan - one of the tournament's lowest-ranked players - but was edged out 10-9 in a thrilling finish.

Speaking to TNT Sports afterwards, shared his assessment of Wilson's performance, stressing that his form wasn't the issue. "I don't think Kyren played that bad, I just think the other guy played well," said the 49-year-old.

"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."

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He applauded Lei's composure and praised his resilience, calling it a "huge asset". Still, 'The Rocket' hinted that Wilson's defeat may have stemmed from misjudged scheduling earlier in the season.

"I always text Kyren through the season because I get on quite well with him," O'Sullivan 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."

He added: "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.

"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 early exit makes him the latest casualty of the notorious 'Crucible Curse', which has haunted first-time champions since the event's 1977 move to Sheffield - none have managed to retain their title.

The World No. 2 began the match on shaky ground, losing the opening two frames. He rebounded strongly to lead 6-3 at the mid-session break, putting himself in a strong position. But his game unravelled in the evening session as Lei surged with six straight frames.

Though Wilson, 33, forced a decider by evening the score at 9-9, 21-year-old Lei held his nerve, producing a superb 66-point clearance to secure victory. The Chinese debutant will now face either Jak Jones or Zhao Xintong, who has just returned from a lengthy ban due to .

O'Sullivan's own tournament begins with a clash against long-time rival on Tuesday. Should he prevail, a meeting with either Zhang Anda or Pang Junxu awaits.

A championship run this year would clinch O'Sullivan his eighth title, making him the undisputed most decorated player of the modern snooker era.