Judd Trump resisted a spirited challenge by Yan Bingtao to creep one step closer to shattering the so-called 'Crucible Curse' and becoming the first first-time champion to retain his world snooker title.
Despite winning six frames in a row to turn a two-frame overnight deficit into a 9-7 lead heading into the decisive session, Trump frequently laboured to shrug off his Chinese opponent until a nerveless final frame century break proved enough to wrap up a 13-11 victory.
Ronnie O'Sullivan shared the opening session of his clash with Ding Junhui to ensure the pair will resume at 4-4 on Saturday, while earlier Mark Williams beat fellow former champion Stuart Bingham, and Mark Selby held his nerve in a final frame decider against Noppon Saengkham.
Trump showed few glimpses of the form which swept him to the title last year and could have faced a much tighter challenge had Yan not missed a simple brown which would have hauled him level at 10-10 at the mid-session interval.
Instead Trump stepped in to clear the colours and nudge two frames clear, and despite a spirited 94 in the next from his opponent, it would prove just enough of a cushion for the 29-year-old to sustain his advantage.
Edging through a gruelling, 50-minute 22nd frame in which Yan briefly got the two snookers he had required to potentially force a re-spot, Trump moved within one frame of victory only for Yan to respond with a superb 130 clearance to reduce the deficit to 12-11.
Despite a few early scares, Trump managed to fashion his superb 127 clearance to finish which will send him into his last eight clash with either Kyren Wilson or Martin Gould in good heart.
Trump said: "It was scrappy and the conditions weren't great but I got over the line which is the main thing.
"It's obviously nice to play well and blow everyone away and play exciting snooker that's pretty to watch, but sometimes you've got to scrap away and that's why I've won six events this year.
"I don't love playing like that, but I think I've got to the age where I'm past caring whether it's pretty or not, it's about getting the job done and winning as many world titles as possible."
O'Sullivan turned a 3-1 deficit against Ding into 4-3 lead, including a fine break of 101, before Ding, a former runner-up, survived a foul on match ball to win the final frame of their quickfire session.
Williams, who will face either O'Sullivan or Ding in the last eight, revealed how a blunt appraisal of his performance from his 13-year-old son Kian spurred him on to beat Bingham and book his place back in the World Championship quarter-finals.
The three-time former winner turned an 8-8 overnight tie into a 13-11 win over the 2015 champion, taking him into the last eight at the Crucible for the ninth time.
Williams said: "I walked in and the first thing he said was, 'why are you so crap?' I'm going to take him on the golf course this afternoon and give him an absolute b******ing because of all the stick he's been giving me these last few days."
Selby, another three-time champion, summoned a 124 clearance in the final-frame decider to see off Thai qualifier Saengkham, who had threatened to add to the growing casualty list of seeds in the tournament.
Selby looked home and dry after a break of 92 moved him 12-10 in front, but Saengkham, who beat Shaun Murphy in the opening round, threatened to repeat the feat as he hauled the match back level with a 90 break of his own.
Selby said: "It's nice to know that when I've got under pressure I've managed to produce again, because that was missing for a few years, especially at the Crucible.
"When I've been asked the question before, sometimes over the last few years I've not really held up, so it's nice to know that it's still there and I'm not going on a downward spiral."
World number 89 Jamie Clarke continued his dream form at the Crucible by establishing a 6-2 overnight lead over fellow qualifier Anthony McGill.