Barry Hawkins holds onto advantage over Ronnie O'Sullivan
Ronnie O'Sullivan remained in deep trouble and at risk of his earliest Betfred World Championship exit since 2009 after Barry Hawkins clung to his lead in their gripping second-round clash.
From 5-3 ahead, Hawkins split Sunday's eight frames with the title favourite to nudge 9-7 in front, needing four more for victory when the match reaches its climax on Monday evening.
Breaks of 68, 118, 82 and 89 from O'Sullivan showed he is scoring well enough - he also had 139, 88 and 103 on Saturday - but Hawkins has clawed his way in front and is fighting to stay there.
Five-time world champion O'Sullivan beat Hawkins 10-1 in the Masters final in January, and was also brutal against the Kent cueman in the 2013 Crucible title match. Revenge for those defeats would taste sweet for the underdog, and O'Sullivan was all business, no nonsense, as he recognised the threat.
Hawkins held his nerve in a tense and deeply tactical final frame of Sunday's session, after making three errors in the previous two that had allowed O'Sullivan to cut his deficit from 8-5 to 8-7, and taking that could prove critical.
O'Sullivan has reached the quarter-finals or better in each of the last six years.
A girl in the front row wore an 'I LOVE RONNIE' T-shirt, and the sense within the arena was that the crowd expected a guns-blazing O'Sullivan fightback.
O'Sullivan can inspire the sort of devotion that the cricketer WG Grace once felt he enjoyed.
Perhaps most spectators in Sheffield had come to see O'Sullivan pot balls, and make centuries, but they gradually warmed to his opponent, a left-hander with a no-frills but effective game.
Early in the first frame of the afternoon, O'Sullivan lanced a terrific opening long red and made 68 but then lost position, played the wrong shot and played it poorly, and Hawkins had a let-off.
From almost the point of no return, the 37-year-old hauled himself back into the frame and won it, an early dagger to the heart for O'Sullivan.
A third century of the match from O'Sullivan settled him, and they split the next two before the interval.
Tickets for the final have been changing hands for upwards of £700, caused no doubt by the O'Sullivan factor.
To lose him at this stage might be considered a blow to the tournament, and he came roaring back after Hawkins swiped the first frame after the mid-session interval with a 65 break.
Momentum was with O'Sullivan heading into the final frame of the afternoon, but safety play let him down, as it repeatedly had done in the frames that Hawkins won, and runs of 41 and 27 saw the two-frame gap re-established.
John Higgins carved out a 10-6 lead over Ricky Walden on the other table, putting the four-time world champion in a strong position to clinch a quarter-final clash against fellow Scot Alan McManus.
The evening session of the tournament's middle Sunday was set to be enthralling, with Judd Trump and Mark Allen in trouble after both had a rotten morning.
Trump became embroiled in a Twitter row when his trophy hopes took a major nosedive.
The 2011 Crucible runner-up was tied at 2-2 with Ding Junhui at the interval in the opening session of their match, before sliding 6-2 adrift.
While in his dressing room during the break, after making a break of 106 to split the opening four frames, Trump objected to a tweet from veteran Welsh cueman Dominic Dale.
Dale wrote, in a tweet he later deleted: "There is a colossal difference in class between Ding and Judd when it comes to cue ball control. It's Judd's biggest downfall."
Bristolian Trump hit back at the 44-year-old by replying: "You are clueless. Watch my first break of 80 something then watch both his frames."
Former semi-finalist Allen fell 7-1 behind against Kettering's Kyren Wilson, but the 30-year-old from Antrim was trying to look on the bright side.
Allen tweeted: "Perfectly poised for a legendary come back. It's first to 13, don't worry!! Ha ha".
Wilson maintained his healthy advantage to take an 11-5 lead into the final session on Monday afternoon.
But that did not tell the full story as Allen staged a courageous comeback to win the first four frames of the evening before Wilson responded in kind.
Allen recorded back-to-back clearances of 122 and 103 - the 55th and 56th century breaks of the tournament - and Wilson mustered only one point in losing the first three frames.
Another break of 66 reduced Wilson's advantage to 7-5, but the interval allowed him to clear his head and he returned with a frame-winning 82 and then took the next.
Wilson shaded a tight 15th frame despite missing the pink and there was an even more extraordinary end in the session finale.
The Englishman needed a snooker with only the colours left, but Allen suffered a double-kiss on the yellow and sent the cue ball into the middle pocket and Wilson eventually prevailed to move within a couple of frames of his first Crucible quarter-final.
Trump trails 10-6 as Ding split the session to protect his four-frame advantage into Monday.
The first four frames were shared, Ding winning the 10th on the black and Trump replying with a 70 break at odds with the bitty nature of the contest.
The next two were also split but Trump lost the 15th frame after getting the snooker he needed, Ding punishing him after he missed the pink.
But Trump took the final frame to raise hopes of another fightback to match that of his first-round victory against Liang Wenbo.