Anthony McGill is four frames away from the semi-finals for the World Snooker Championship ©Getty Images

Mark Selby and Anthony McGill hold leads in their respective quarter-finals as the last eight got underway today at the World Snooker Championship in Sheffield.

England's Selby holds a four-frame lead over Mark Williams of Wales in a clash featuring a pair of three-time world champions.

Selby leads 6-2 at the Crucible Theatre, but there is still a long way to go in the best-of-25-frames match.

Williams ended the day on a high note at least, with a 111 break to win the eighth frame.

Eight frames have been played in the all-English encounter between Judd Trump and Shaun Murphy - also both former champions - and the score is 4-4.

Anthony McGill of Scotland produced the two biggest breaks of the day - 130 and 126 - en route to establishing a 9-7 lead over Englishman Stuart Bingham.

Bingham, the 2015 champion, had been 6-4 ahead, but McGill's confidence appears sky high after he knocked out reigning champion Ronnie O'Sullivan of England - who was chasing a record-equalling seventh world title - in the last round.

Kyren Wilson from England, last year's runner-up, and 2010 champion Neil Robertson of Australia are all square at 8-8 in the other quarter-final.

There were 11 century breaks today and the quarter-finals are due to be completed tomorrow.