Defending champion Mark Selby was left with plenty to think about overnight following an enthralling first session of his Betfred World Championship semi-final with Ding Junhui.
There was little to split the pair in Sheffield on Thursday before Ding, who lost to Selby in last year's final, won the final three frames to secure a 5-3 advantage.
They shared the opening four frames of the best-of-33 clash at the Crucible, with Ding twice edging ahead.
The 30-year-old Chinese player cleared up with a break of 76 in the first and then took the third with a run of 84 after Selby had again let him back in.
This is shaping up to be 👌
— World Snooker (@WorldSnooker1) April 27, 2017
Ding fires in a century [110] to end the session 5-3 up on Selby in the semis! #ilovesnooker pic.twitter.com/1b5uMb7UeO
Selby responded on both occasions, producing an audacious pot on a red on his way to a break of 68 in the second and then falling one point short of a century in the fourth.
The contest became a far more tactical affair following the mid-session interval and Selby edged in front for the first time at 3-2 following a frame lasting almost 34 minutes.
The world number one had cruised through to the last four, dropping only 11 frames in comfortable victories over Fergal O'Brien, Xiao Guodong and Marco Fu but, as expected, Ding was proving to be a far more formidable opponent.
He pegged back Selby after another lengthy frame of safety exchanges before runs of 56 and 50 in the seventh saw the world number four restore his lead.
Ding then ensured he would take a slender advantage into the second session by wrapping up the final frame with the first century of the match (110).
"This is the biggest shot of the match tonight."
— World Snooker (@WorldSnooker1) April 27, 2017
Massive frame for @TheHawk147 to end the session! 👊 #ilovesnooker @Betfred pic.twitter.com/y8edwtx62F
Four-time winner John Higgins held the initiative in the other semi-final after having the better of a scrappy encounter with Barry Hawkins.
The 41-year-old, playing in the last four at the Crucible for the first time since he last won the tournament in 2011, led 5-3 going into Friday's second session, although he may feel his narrow advantage should have been more.
Both players had plenty of opportunities among the balls early on, but it was Higgins who took control as he won three untidy frames in succession.
The Scot then had a wobble, missing frame ball while on a break of 69 to give Hawkins a chance to cut the deficit to two.
World number seven Hawkins set about the task superbly and was on course to clear up before failing on the final pink and allowing Higgins to head into the interval 4-0 up.
Hawkins, runner-up in 2013, appeared unable to settle before the break, but he finally got himself on the scoreboard after the restart, producing breaks of 62 and 71 to halve Higgins' lead.
Higgins, ranked sixth in the world, then recovered to take the seventh after missing another frame ball, before 38-year-old Hawkins wrapped up the final frame with a break of 74 to pull back to within two.
