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Day overturned a big deficit from the first session
Wales' Ryan Day ended John Higgins's reign as world champion as he held his nerve to secure a 13-9 win in their second-round clash at the Crucible.
The players resumed at 8-8 and Day hit the ground running as he took the first three frames of the session in quick succession to surge into an 11-8 lead.
Higgins, who criticised organisers for the condition of the tables, kept his hopes alive with an 83 break.
But Day sealed the biggest win of his career with a nerveless display.
Higgins, who beat Mark Selby in last year's final to win his second world title, enjoyed leads of 4-0 and 6-3 earlier in the match.
The Scot was hoping to become only the third player to successfully defend the title, but he looked looked short of his best form for large parts of the match.
Ryan totally deserved to win but it was a lottery whenever you were playing off any cushions
His frustration with the unpredictable bounce off the cushion was clear in the second session when he punched the table and was booed by some sections of the crowd.
Speaking after the match, Higgins did not mince his words when asked about the condition of the tables.
"I spoke to the tournament director (Mike Ganley) about it. We are playing on the same cloth for eight days and they are going to re-cover them on Saturday night I think," he said.
"They should be re-covered before the second round. We've always had these problems.
"We are talking about the biggest tournament in our lives and the answer I get back is that they haven't got the manpower to re-cover the tables before the second round.
Day reached the last eight at The Crucible for the first time
"It's flabbergasting and I let it get to me and it's a lesson I have to learn.
"The cushions are totally unplayable.
"Let me stress, Ryan totally deserved to win and the conditions are for both players but it was a lottery whenever you were playing off any cushions.
"It's really pretty pathetic that they are undermanned and can't re-cover them until Saturday night but that is too late for the likes of myself.
"I don't think the tournament director is doing his job correctly. We are not asking a lot, it should be easily fixed."
World Snooker responded in a statement: "Along with our partners, we are determined to ensure that we provide the best possible playing conditions at the 888.com World Snooker Championship.
"This is the longest tournament that we run. Two years ago we decided to bring in an extra re-cover of the tables after the second Saturday of the event. Previously the tables were not re-covered until the semi-final stage."
Day, in contrast, kept his composure and looked sharp when in amongst the balls.
The world number 16 even had the luxury of trying to play for a maximum 147 break in the final frame, only to see a difficult red rattle in the jaws of the pocket.
It left with Higgins with the simplest of chances to try to resurrect his challenge, but the world number one somehow missed from point-blank range.
Day gratefully accepted his unexpected second chance and made a 69 to seal the biggest win of his career.
The 28-year-old said he could sympathise - up to a point - with Higgins's annoyance at the state of the tables.
"I understand what John was saying but I just tried to get on with it," he said.
"There's not a lot you can do about it, we have all played on the same table. I think I dealt with it best.
"I don't think it was all that bad and even a brand new cloth has bad bounces."
It is the first time Day has reached the quarter-finals, where he will meet either Stephen Hendry or Ding Junhui, at The Crucible.