World Snooker Championship 2013: O'Sullivan leads Carter
Defending champion Ronnie O'Sullivan holds a 9-7 lead over Ali Carter in their World Championship last-16 match at the Crucible.
In a repeat of last year's final, O'Sullivan led 5-3 after Saturday's opening session and a break of 86 saw him extend that advantage to 6-3.
But Carter won four of the next five frames to make it 7-7, before O'Sullivan took the last two frames.
Meanwhile, Ding Junhui recovered from 6-2 down to lead Mark King 9-7.
"It was arguably the most entertaining and gripping session of the Championship so far.
"Four breaks of more than 70, including a century from O'Sullivan, sounds impressive, yet the defending champion didn't entirely convince, looking pressured and uncomfortable at times.
"Carter punished three glaring potting errors with frame-winning breaks as he levelled at 7-7 from 5-1 down, but he couldn't push on from there, a missed opportunity perhaps, as the 'Rocket' recovered his poise to share the session and retain his two-frame cushion."
He needs to win only four more frames in the final session on Monday to move into the quarter-finals and set up a meeting with Premier League winner Stuart Bingham or world number 16 Mark Davis.
O'Sullivan, who beat Marcus Campbell in the first round, took the opening frame of the second session 86-0.
Fellow Englishman Carter responded with efforts of 73 and 87 to reduce the gap to one, but O'Sullivan's break of 105 in the 12th frame saw him restore his two-frame advantage at 7-5.
Carter, the 16th seed, pulled it back to 7-7, before O'Sullivan made breaks of 73 and 86 to end the session as he started, two frames ahead.
China's Ding, a semi-finalist in 2011,produced a fine comeback on the second day of his match against King.
Ding trailed 6-2 after the opening session but made breaks of 59, 98, 74, 63 and 103 as he won seven of the eight frames in the second session to lead 9-7, only four away from the winning target of 13.
King, 30th in the world, defeated seventh seed Mark Allen in the first round but now needs to produce a spirited performance in the final session on Monday to eliminate world number nine Ding.