Kyren Wilson stays in the hunt
London - Five-time world champion Ronnie O'Sullivan holds a 5-3 lead over Mark Selby in the other semifinal.
Wilson trailed 6-2 overnight in the best of 33-frame clash, but he hit two centuries to win six of the eight frames at Sheffield's Crucible Theatre.
McGill, in his first world semifinal, potted just 47 balls in the session as the battle for a place in the final headed to a decisive last session.
Wilson, who beat defending champion Judd Trump in the quarterfinals, resumed in determined style as he attempted to claw back the deficit.
He took the opening frame with a break of 100, the first century of the semi-finals.
An error by McGill handed Wilson the chance to make it 6-4 with a visit of 77.
Although McGill stopped the rot by taking the 11th frame after his opponent had missed a difficult red, another mistake by the Scot during a safety exchange saw Wilson reduce the gap once again with a 73 break.
Five-time world champion Ronnie O'Sullivan holds a 5-3 lead over Mark Selby in the other semifinal.