Alexander Levy picked up seven shots in his opening 12 holes to race into the Italian Open lead as play was again affected by the weather.
Due to torrential rain and the threat of lightning on Friday, the majority of the field had to complete round two on Saturday, with Chris Paisley maintaining his overnight lead.
The Englishman reached the halfway stage 13 under, one clear of Danny Willett, with Rikard Karlberg and Chris Wood a further two shots back.
Paisley was only able to complete nine holes of his third round, though, as bad light halted play at 19:30 local time - the 30-year-old slipping into a tie for second after going out in par.
Levy took the overall lead after a stunning front nine, the Frenchman picking up an eagle at the first before five birdies arrived by the turn.
Three successive pars on the back nine left him at -14 when the hooter sounded, Levy one clear of Paisley and three others heading into Sunday.
Home favourite Francesco Molinari, Chris Hanson and Masters champion Willett are level with the former leader, but all have holes still to play in round three.
An Byeong-hun heads a group of five on 12 under after picking up five strokes up to the 13th, but his progress was halted as the clouds came in, reducing the light levels in Monza.
Twenty two players are separated by four shots ahead of the final day, which will once again see the majority of the field complete one round before starting another in the battle for the title.