Defending champion Judd Trump must come from behind to keep alive hopes of retaining his Crucible crown, while five-time winner Ronnie O’Sullivan also has plenty of work to do.
World number one Trump, chasing a seventh ranking title of a remarkable season, is just three frames from elimination after falling 10-6 behind in his best-of-25 quarter-final tie with Kyren Wilson.
O’Sullivan had earlier slipped to a 6-2 deficit against fellow veteran Mark Williams following the opening session of their heavyweight clash in Sheffield.
Three-time winner Mark Selby has the semi-finals in his sights after building a commanding 11-5 lead over Neil Robertson, while Anthony McGill has complete control of the other last-eight match, holding a 7-1 advantage over Kurt Maflin.
Trailing 5-3 from the opening session, a frustrated Trump continued to be kept at arm’s length by Wilson as the pair initially traded frames.
Wilson responded to Trump’s knock of 73 with a break of 65 to maintain his two-frame advantage.
Trump, who beat John Higgins in last year’s final, again reduced the deficit to a single frame but then blew an excellent opportunity to level at 6-6 by missing a costly final black.
The pattern continued as Wilson ensured he could not trail overnight with a superb 94, the highest break so far of a century-free contest, to go 8-6 ahead. He then pulled away, taking the final two frames to leave Trump facing an uphill battle on Tuesday.
O’Sullivan must also produce a comeback following an inspired display from Williams.
Welshman Williams, seeking a fourth world title of his own, won five consecutive frames to take a firm grip on the contest.
There had been nothing to separate the experienced duo before the mid-session interval as they shared the opening four frames, which included an O’Sullivan century.
Who predicted this?
Three-time champion @markwil147 rounds off the session with 1️⃣3️⃣0️⃣ after runs of 72 & 56 since the interval.
— World Snooker Tour (@WeAreWST) August 10, 2020
But O’Sullivan, who controversially questioned snooker’s next generation after beating Ding Junhui on Sunday by saying he would need to “lose an arm and a leg” to fall out of the top 50, was second best on the resumption of play and left with plenty to ponder.
Williams edged a scrappy fifth frame before propelling himself into a healthy position with breaks of 72, 56 and a superb 130.
Meanwhile, Selby holds the upper hand against 2010 champion Robertson.
Selby reeled off five consecutive frames to race ahead but was pegged back to 5-3 during the afternoon.
The opening frame had lasted a marathon 58 minutes and progress remained slow in a low-scoring slog of an evening session.
Selby, champion in 2014, 2016 and 2017, eventually ended the day six frames in front and with a last-four spot within touching distance after finishing with a fine break of 76, one of only two 50-plus breaks following the resumption of play.
In the battle of the qualifiers, McGill has complete control after dominating the opening session against Norwegian Maflin.