Three-time winner Mark Williams reached the final last year and would become the oldest world champion if, at 51, he could win the tournament for a fourth time.
His last-16 opponent Barry Hawkins took the opening frame of their match with a break of 127, and the pair alternated frames with Williams making a 124 in frame four and 65 in frame six.
The Welshman moved ahead for the first time by taking the seventh frame, only for Hawkins to win the last of the session, helped by a run of 73, to draw level at 4-4.
Their match resumed at 19:00 BST on Friday and will be played to a finish on Saturday evening.
The eagerly-awaited match between China’s first ranking event winner Ding Junhui and its first world champion Zhao Xintong is also level at 4-4.
In a tie which could become the most-watched match in snooker history because of its appeal to the Chinese audience, the pair alternated the opening five frames, with Xhao’s break of 116 in frame four the highlight.
Zhao won the sixth and seventh frames, but Ding sneaked the eighth on the black, by a scoreline of 62-61 to leave it level before the second session on Saturday afternoon (14:30 BST).
The tie between 2024 winner Kyren Wilson and former world number one Mark Allen is set for a thrilling finish on Saturday morning (10:00 BST).
Northern Ireland’s Allen had been 5-0 ahead on Thursday, before Wilson won the final three frames of the session.
The Englishman maintained his form by winning three in a row, following breaks of 71, 52, 112 to lead 6-5, but an excellent match swung again, with Allen winning four of the last five frames to hold a 9-7 advantage.
The highlight was a break of 140 from Allen in frame 15, the second time he has made that score in this year’s Crucible event.