Mark Selby finally cracked at the Crucible as the defending champion lost in the first round – and Ronnie O’Sullivan could follow him out of the tournament on Sunday.

A stunning opening day of the Betfred World Championship saw defending champion Selby bundled out 10-4 by veteran Joe Perry, while O’Sullivan was unusually subdued as he fell 6-3 behind against Stephen Maguire.

If O’Sullivan can somehow turn that match around on Sunday morning, he will know the exit of Selby bolsters his chances of landing a sixth world title.

Selby, the man whose game was described as “granite” by runner-up John Higgins after last year’s final, saw his defence hit the rocks.

He had been bidding to become just the third player, after Steve Davis and Stephen Hendry, to reel off three successive world titles since the tournament made Sheffield its permanent home in 1977.

Instead Perry marches on, saying: “I’m delighted, I’m chuffed. When the draw came out it’s one of your two worst nightmares.

“When you beat the world number one, world champion, in any tournament it’s a great feeling. To do it at the Crucible makes it even more special.”

Selby said: “I lost it really in the first session. My safety wasn’t up to scratch and every time I made a mistake he punished me heavily.”

He paid tribute to the talent of his conqueror, saying: “He’s underachieved if anything. He should have won a lot more than he’s won. I’ve always rated him as a top player.

“The last three or four years I’ve had some good success here so I can’t complain.”

Perry, 43, led 7-2 after the morning session. But comebacks are a Selby speciality so Perry was taking nothing for granted when they returned in the evening. Instead of a full-on assault on his lead, however, he was met with more misfiring from Selby.

Perry reached the Crucible semi-finals in 2008, losing a gripping match 17-15 to Ali Carter, and has dipped to 22nd in the world rankings.

Selby tops that list and has done so at the end of each season since 2012/13, but he leaves snooker’s most famous stage empty-handed this time.

It seemed inconceivable that Selby and O’Sullivan would both bow out on the opening weekend, but that is now a distinct possibility.

Ronnie O’Sullivan reacts during his match with Stephen Maguire
Ronnie O’Sullivan reacts during his match with Stephen Maguire (Richard Sellars/PA)

Maguire kept his cool as O’Sullivan flexed his muscle with back-to-back centuries at one stage, and the Glaswegian took the final two frames of the day to build a richly-deserved advantage.

O’Sullivan has not been beaten in the opening round in Sheffield since losing 10-6 to Marco Fu in 2003, but a repeat was looming large.

He lost his composure during the eighth frame, playing a poor positional shot and following up by rushing an attempted safety and getting it horribly wrong. O’Sullivan stuck his tongue out, annoyed at himself. It was that sort of day for him. For Selby it was even worse.

Elsewhere, Graeme Dott carved out a 6-3 lead over Ali Carter, and debutant Lyu Haotian was ahead by the same margin against Marco Fu. Kyren Wilson moved 7-2 clear of Matthew Stevens.