Gilbert knocks out defending champion Williams - best shotsBetfred World Snooker ChampionshipVenue: Crucible Theatre, Sheffield Dates: 20 April-6 MayCoverage: Watch live on BBC One, BBC Two, Red Button, iPlayer, Connected TV, BBC Sport website and BBC Sport app.
Defending champion Mark Williams became the second three-time champion to go out of the World Championship in Sheffield on Saturday, following Mark Selby's earlier shock defeat.
Welshman Williams, who was in hospital on Friday with chest pains, lost 13-9 to David Gilbert in the second round.
Williams became unwell after falling 5-3 behind in the first session, before returning to the Crucible on Saturday.
Selby had earlier suffered a surprise 13-10 loss to Gary Wilson.
Former potato farmer Gilbert's win over Williams, 44, included stroking in a tremendous 139 clearance, and he will now play either Barry Hawkins or Kyren Wilson.
An emotional Gilbert said: "It was one of my best performances. I really enjoyed it from start to finish. I felt so calm and comfortable in the last session.
"I hope Mark is all right but I was focused on myself and to come to the table and believe in myself. If I can keep going I will cause some people some grief."
'Felt like someone stabbing me in chest'
Williams said of his health scare: "I was having pains in my chest and could not stick it, I did not know what it was and went straight to A&E to get it checked out.
"Thank God the doctors said it was not a heart problem. I will go home and see the doctor and get a full MOT.
"I was frightened because I did not know what it was. It felt like someone was stabbing me in the chest. I can still feel it now but it is nowhere near as bad as it was on Friday afternoon."
He added: "I got back to the hotel last night at 11pm, I was sleeping all night then played my match and slept again.
"You cannot withdraw from this tournament, maybe if it was a smaller one but you can't pull out of this. I am still proud of myself for carrying on. I played dreadful really.
"The draw has opened up for people like Judd [Trump] and Ding [Junhui]. They will be thinking it is the best time to get to the final."
Earlier on Saturday Selby, 35, fell 5-3 and 9-7 behind before levelling at 10-10.
But qualifier and fellow Englishman Wilson, 33, held himself together superbly by claiming three frames on the trot, including a cool 92 break.
In the pick of the second round matches, between two former finalists, Englishman Trump opened up a 5-3 lead over China's Ding.
Trump made two breaks of 61 and further runs of 57 and 50 for a two-frame advantage and the pair resume on Sunday afternoon.
Two-time semi-finalist Stephen Maguire also ended the challenge of amateur James Cahill with a thrilling 13-12 victory to reach the last eight.
Cahill, who created the biggest shock in Crucible history by beating world number one Ronnie O'Sullivan in the first round, was trailing throughout the contest before going 11-10 in front.
Both players became increasingly nervy and Blackpool's Cahill forced a final-frame decider, but Scotland's Maguire managed to hold himself together to progress and will face either Trump or Ding next.
Four-time champion John Higgins won the last three frames to escape 4-4 after the first session of his second-round match against 2015 winner Stuart Bingham. The pair resume on Sunday afternoon.
Taxi for Selby as Wilson relishes 'best result of my career'Superb Wilson stuns three-time champion Selby - best shots
Selby won the China Championship in September but has struggled to find his best form since, usurped at the top of the world rankings by Ronnie O'Sullivan and failing to reach another final this season.
He continued his poor recent record in Triple Crown events, last winning consecutive games at the World, UK or Masters in 2017 when he won the title in Sheffield.
Wilson is a former taxi driver who is playing in the World Championship for only the second time.
He gained a measure of revenge for his 10-2 thrashing by Selby in the 2015 China Open final to set up a last-eight meeting against Ali Carter or Zhou Yuelong, both of whom also qualified.
Wilson described the surprise victory as "the best result of my career".
Asked if he can go on to win the tournament, Wilson replied: "Who knows? I was close to quitting many times. I always knew deep down I was good enough and could make a living in this game.
"There are times you are literally all over the place, can't pot a ball and think, 'What's the point? I can't even play'. It's a strange game."
Selby said he did not think his performance was "that bad", adding: "Gary played well and deserved to win. I felt I missed the boat yesterday and the run of the ball in the first two sessions didn't go my way.
"I'll have a month and a half off now, go on holiday and forget about the season."
