Mark Selby turned the tables on a frustrated Ronnie O'Sullivan as he fought back to take a 9-7 lead in their World Championship semi-final.

Selby, who had managed to cling to O'Sullivan's coattails at 5-3 down by winning the final frame of a difficult first session on Wednesday, took the first four on Thursday afternoon before holding his nerve to win the second and last after the interval for a 6-2 return.

O'Sullivan, who had been decidedly unhappy with the amount of kicks he had suffered on Wednesday, was left shaking his head again as another cost him an easy black when he was in pole position to take the first frame.

Selby eventually got the better of a prolonged bout of safety play to edge himself to within a single frame of the Rocket, and they were level after the next when he put together a break of 97, his highest of the match.

O'Sullivan's fluency had deserted him and having been among the balls twice only to miss blue and then black, he saw Selby clinch a fourth successive frame to take a 6-5 lead after sinking a fine long red.

He made it a clean sweep before the mid-session interval after O'Sullivan had once again got in first, but it was Selby who faltered on the resumption as his opponent took full advantage of a poor attempt at a red to rattle in a decisive 87 and pull it back to 7-6.

A break of 61 following a missed blue by the Rocket proved sufficient for Selby to restore his two-frame advantage, but after he had left a difficult red in the middle in the 15th, O'Sullivan compiled a run of 82 without reply to peg him back once again.

He was left rapping his knuckles on the table, however, after failing to drop a difficult pink as the session drew to a close, in the process handing Selby the opportunity to make it 9-7 with a break of 76.

In the morning session, Kyren Wilson significantly improved his chances of making it to the final after eradicating Anthony McGill's 6-2 lead in some style.

The Englishman made two century breaks as he fought back to level the match at 8-8 with McGill managing just 47 pots in the entire session.

Wilson signalled his intent from the off with breaks of 100 and 77 to take the first two frames and although McGill steadied the ship to make it 7-4 and then 8-5, his opponent was not to be denied.

An impressive clearance of 116 after McGill had left a red in the jaws following a re-rack was decisive in the 14th, and the 15th followed courtesy of breaks of 44 and 46 before he wrapped up a good morning's work with a 76-0 victory in the last of the session.