O'Sullivan in charge while Williams recovers against Higgins

Seven-time winner Ronnie O'Sullivan opened up a commanding 6-2 lead over Si Jiahui in the first session of their World Championship quarter-final.

O'Sullivan, who is bidding for a record eighth title in the modern era, took a scrappy opener before Si responded with a wonderful century break.

However, the 22-year-old from China uncharacteristically missed a series of pots to allow 'The Rocket' to pull clear at 4-1 with three half-centuries.

While Si responded with a 60 of his own to briefly reduce his arrears, another miss, on a black on its spot, proved costly as O'Sullivan pinched the seventh frame.

The Englishman concluded the session with a stylish 121 break to underline his superiority.

In Tuesday afternoon's other last-eight contest Judd Trump produced a superb display of potting as he compiled his 101st and 102nd century breaks of the season to go 5-3 up on Luca Brecel.

Their best-of-25 encounters will continue on Wednesday at 10:00 BST.

World number one Trump is now only one away from equalling the record of 103 century breaks in a single campaign, set by Neil Robertson in 2013-14.

Trump had raced 5-1 ahead, however, Belgium's Brecel, who won in Sheffield two years ago, fought back with breaks of 68 and 128 to leave the match delicately poised.

Meanwhile, four-time champion John Higgins holds a 5-3 advantage against Mark Williams in their second Crucible meeting since the Welshman defeated the Scot in the 2018 final.

Williams, 50, became the oldest man to reach the last eight at the famous Sheffield venue since Steve Davis did so at the age of 52 in 2010, while Higgins turns 50 on 18 May, 13 days after this tournament's final.

Both men received a fantastic standing ovation when introduced to the crowd, with the spectators then treated to some high-quality snooker.

A break of 69 took Higgins ahead, but Williams should have levelled, only for the Scot to snatch the frame on the black following a run of 65.

An effort of 72 gave the Welshman his first frame, only for him to miss a brown in the fourth frame, and that proved costly as Higgins took the first of three frames in a row.

Being 5-1 ahead, Higgins would have hoped to stretch his lead, but Williams responded well with breaks of 104 and 59.

The pair who have played 42 times on the main tour since they turned professional in 1992, will continue their latest encounter at 19:00 BST.

In the morning session's other match, China's Zhao Xintong took control of his quarter-final tie with Chris Wakelin.

The Englishman, who came through two qualifying rounds to get to the Crucible, eliminated 2010 world champion Neil Robertson in the first round of the main tournament and then defeated former world number one Mark Allen in the last 16.

Wakelin, 33, made a break of 93 to take the opening frame, but 28-year-old Zhao then dominated to win six in a row, although Wakelin took the last to trail 6-2 before that match resumes at 19:00 BST.

Zhao, a former UK Championship winner, was one of 10 players from China to receive a ban in a match-fixing scandal.

He did not directly throw a match, but accepted charges of being a party to another player fixing two matches and betting on matches himself. Zhao - who served a 20-month ban for those offences - is the only of the 10 players sanctioned in the scandal to have returned to action.

As a result of the ban, he lost his place on the World Snooker Tour, although he has already ensured he will be back on the tour full-time next season.

For this tournament, he is officially classed as an amateur and this is his seventh match of the competition, after he had to fight through four qualifying rounds to reach the main draw.