Ronnie O'Sullivan rallied with two century breaks to draw level at 4-4 with John Higgins in their World Championship semi-final.
O'Sullivan trailed 3-0 as the Scot came out of the blocks fast at the Crucible, but the world number one produced clearances of 116 and 107 on his way to restoring parity.
Both players had opportunities to open their account in the first two frames, but it was O'Sullivan who needed extra time to settle, and Higgins held his nerve with a decisive 50 break to take a 2-0 lead.
Higgins looked like compiling another frame-winning break in the third, but he missed a straightforward black before complaining that someone in the crowd had moved in his eyeline.
But O'Sullivan ran out of position after making 32 in reply, his frustration evident as he stamped his cue on the floor before missing a red that would cost him dear.
O'Sullivan, however, was now starting to find his groove.
A 70 break gave him impetus before the interval and scores of 45 and 54 in the next cut the deficit to one frame.
O'Sullivan capitalised on a safety error to produce his first century of the match before Higgins stopped the rot to secure a close penultimate frame on the pink.
But O'Sullivan was not to be denied and ensured he would go into Friday's second session level with another superb century.
In the other semi-final, Judd Trump dominated the early stages to take a commanding 7-1 lead over Mark Williams.
Trump's long potting was a constant theme of a scrappy opening session as three-time champion Williams struggled to find any sort of fluency.
The Welshman's only success came in a long fourth frame, and he appeared unhappy with the table at the end of it when he rolled a ball down the cloth to check its condition.
Following a rerack in the opening frame, Williams' misery began when he went into a bunch of reds after potting a blue and one of them ended up in the bottom pocket.
Trump, the 2019 world champion, took advantage with 49 in reply before a long brown after some safety exchanges sealed the frame.
Successive breaks of 70, the first one benefiting from another Williams in-off, gave Trump a 3-0 lead before a see-saw fourth frame which lasted over 33 minutes.
Williams made heavy weather of his first success after a well-compiled 46 had put him in the driving seat, Trump almost threatening to get the two snookers needed to poach the frame.
It was the same story, however, after the interval as Trump prospered from range and Williams suffered another crucial in-off to dent his recovery hopes.
Trump won a messy fifth frame and came out on top in another safety battle in the sixth.
A 62 break gave Trump the next frame before more caution led to the second rerack of the session.
Trump was looking increasingly confident and produced breaks of 53 and 41 to extend his lead to six, leaving Williams with a mountain to climb in Friday's second session.