Ronnie O'Sullivan tonight claimed Stephen Hendry could be the first in a line of players to quit snooker as he complained about "relentless" demands on players.

Any lingering doubts that O'Sullivan might not have the form or the temperament to land a fourth World Championship title were emphatically dispelled as he beat Neil Robertson 13-10 in the Crucible quarter-finals.

Robertson's title dream was crushed on a day when O'Sullivan played at times exquisitely to close out victory over the Australian.

At the age of 36 years and three months, O'Sullivan would become the oldest world champion since Ray Reardon triumphed aged 45 in 1978.

Matthew Stevens stands in his way of a first appearance in the final since 2008, when the game's most thrilling player lifted the Crucible trophy for a third time.

Stevens completed an 11-frame winning streak as he put paid to his friend Ryan Day's hopes with a 13-5 victory.

And the final match tonight saw Ali Carter resist a determined fightback from Jamie Jones to win by 13-11.

O'Sullivan has threatened to retire on many occasions, and reacting to Hendry's move to quit and promote pool in China, the three-time world champion said: "I'm not surprised really. I'm pleased he has because he has nothing to prove in the game."

"Snooker has changed in the last couple of years and I think it suits certain people but it's not going to suit a lot of other people.

"I know Stephen's retired and you might see a few more retiring because of it, because it's a relentless schedule and until they get it right, it's very difficult."

Robertson had little answer to O'Sullivan's brilliance as the Chigwell showman won the opening six frames of the day to surge from 5-3 behind to 9-5 in front.

Robertson cut that to 9-7 by the end of the session, and when they returned O'Sullivan was at times imperious, making runs to 104, 71, 100 and 59 to counter Robertson's 50, 89 and 77.

Robertson, the 2010 champion, said: "A lot of people thought this was maybe the final. Ronnie handled it better than me. He seems really focused. He'll definitely take some stopping."