Judd Trump has a health lead in his semi-final ©Getty Images

Judd Trump has raced into a 7-1 semi-final lead at the World Snooker Championship, while Ronnie O'Sullivan and John Higgins are tied at 4-4.

England's Trump, the world champion in 2019, has a sizable advantage in the first-to-17 match against Mark Williams.

Trump won the opening three frames of the untidy affair.

Welshman Williams, a three-time world champion, won frame four, but Trump closed out the session with four straight frame victories to take control of the semi-final.

Neither player could post a century.

Englishman O'Sullivan recorded two against Scotland's Higgins, including a 107 break in the final frame of the day to level the scores at 4-4.

Scotland's Higgins had led 3-0, before O'Sullivan fought back to level pegging and the duo exchanged wins in the closing two frames of the session.

All four semi-finalists are former world champions for the first time in the history of the event.

The three-day semi-finals are due to continue tomorrow at the Crucible Theatre in Sheffield.