Ronnie O'Sullivan leads Mark Selby after the opening session of their semi-final at the World Snooker Championship ©Getty Images

Five-time champion Ronnie O'Sullivan leads Mark Selby by two frames after a scrappy opening session of their semi-final at the World Snooker Championship.

O'Sullivan will resume tomorrow with a 5-3 advantage over Selby, a three-time winner of the event at the Crucible Theatre in Sheffield.

Scotland's Anthony McGill will take a 6-2 lead into the second session of his last four encounter with England's Kyren Wilson.

O'Sullivan, who caused controversy earlier this week after he criticised the standard lower down the world rankings, was the better of the two players as he capitalised on the errors made by Selby.

The world number six scored the highest break of the match so far, an 85, to take a 3-1 lead and won frame five to exert further control over Selby.

Selby, playing in his first World Championship semi-final since he won the title in 2017, pulled one back before O'Sullivan re-established his three-frame lead.

Both players struggled to close out the last frame of the session before it was eventually won by Selby, who trails by two despite failing to hit a break over 50.

McGill, the world number 39, is on course to shock Wilson - ranked 31 places higher - after dominating large parts of the first eight frames.

The Scottish player went 3-0 in front before Wilson got on the board, and took the next two as he threatened to open up a potentially decisive lead.

A miss from McGill allowed Wilson to make it 5-2 before the Scot won the last.