Seven-time world champion Ronnie O’Sullivan made a strong start to his last-16 match against Wales’ Ryan Day and holds a 5-3 advantage.
The 48-year-old Englishman is on course for an eighth Crucible title, which would move him clear of Stephen Hendry’s mark of seven successes.
Day is aiming to get into the World Championship quarter-finals for a fourth time, after losing in that round in 2008, 2009 and 2012.
He has played O’Sullivan here before, losing 13-10 having been 9-7 ahead in their last-16 tie in 2006, with Day admitting that loss had hurt.
“This place gives you lots of great memories and lots of scars,” said Day on Wednesday. “That was certainly one of the scars. It’s not physical on your skin, but it is lodged away somewhere deep in your mind.”
O’Sullivan, who thrashed 22-year-old Welsh qualifier Jackson Page 10-1 in the first round, made breaks of 123 and 84 in the opening two frames, although world number 18 Day took the next two frames.
Breaks of 83 and 51 helped O’Sullivan go 4-2 in front, Day responded with a break of 115, but O’Sullivan restored his two-frame advantage with a 92 in the last frame of the session.
The match is the best of 25 frames, so first to 13, and will resume at 19:00 BST in the evening session before being completed on Monday from 14:30.