Adrien Saddier led by one shot at the halfway stage of the weather-affected Omega European Masters after firing rounds of 62 and 65 on a marathon second day in the Swiss mountains.
The race to catch up following Thursday's lengthy fog delays saw Frenchman Saddier play 36 holes on Friday, having been unable to start his first round on day one.
After carding an eagle and six birdies in a flawless first round in the morning, Saddier added a 65 that contained six birdies and a single bogey to reach 13 under par.
Many players had to return to the course on Saturday morning to start or complete their second rounds but no-one was able to catch Saddier at the top.
Defending champion Matt Wallace was Saddier's nearest challenger one shot behind after following up his opening 65 with a second-round 63 to get to 12 under.
Wallace's fellow Englishmen Jordan Smith and Richard Mansell, and South African Thriston Lawrence shared third place on 11 under.
Saddier started his second round from the tenth tee and picked up his first birdie from six feet on the par-three 11th.
The 33-year-old, who claimed his maiden DP World Tour win at the Italian Open in June, saved par from 27 feet on the par-three 13th to keep his card clean before making back-to-back birdies at the 17th and 18th to turn in 32.
His first bogey of the tournament arrived on the first but Saddier bounced back with a chip-in birdie at the third before gains on the seventh and ninth handed him the solo lead.
Saddier said: "I'm pretty happy. It was a long day, to be honest.
"I got a good start this morning - the momentum was good on the first nine and then I just kept holing the putts.
"It was a good day and we like this kind of day. It was just nice to finish with a birdie."
Wallace, who made 15 birdies and three bogeys on Friday, said: "I had three great nines. I would put it that way.
"The first nine this morning wasn't very good but I managed to get it round and then I found something on the back nine.
"I played really nicely this afternoon.
"I said to myself a few times out there today that I'm the defending champion so let's try to keep it that way."
