The Englishman was in the running for the Claret Jug at St Andrews last week after two rounds, eventually finishing four shots off winner Zach Johnson, and his hot streak continued in Crans on Friday.
Willett’s 62 meant he matched the low-36 hole tournament record score of 127 but 36 players were unable to finish their second round as electrical storms brought a premature end to play.
The 27-year-old opened with three birdies and reached the turn in 30 before continuing to make hay down the back nine, despite a bogey on the 12th, to clinch a slender advantage over the South Korean pair of Yang Yong-eun and Baek Seuk-hyun.
“I had a couple of bad swings coming down the last two holes but it was a very good day,” Willett said after moving to 13-under par.
“To get out and birdie the first three in a row, which are the not easiest holes on the course, and then I just kept going — playing some good golf, hitting it in there pretty close and holing out inside 10 to 12 feet.
“It’s always a low scoring week, you know that, and mentally that’s quite good. You can’t just let up and shoot level par and that be good enough.
“You’ve got to take the golf course on because probably somewhere near 20-under par is going to be winning.”
Yang’s 63 made him the pick of the early starters and he entered the clubhouse with a three-shot lead before Baek joined his compatriot on 12-under thanks to a second straight blemish-free round.
Marcus Kinhult ended on nine-under and overnight leader Gregory Havret only picked up one stroke and finished the 36 holes on eight-under alongside Raphael Jacquelin, Rikard Karlberg, Richard Green, David Lipsky and Marcus Fraser.
Havret only held the lead on Thursday night because Tyrrell Hatton found water en route to a triple bogey to close out his first round, but the Englishman had put that behind him with a blistering start yesterday. He turned in 30 to reach the leaderboard’s summit before dropping four shots in eight holes to join the clutch of men one shot behind Havret and co.
Lee Westwood is three-under after shooting a 69 while pre-tournament favourite Sergio Garcia carded a 70 to stand at one-under and should make the weekend with the projected cut at level par.
Michael Hoey slipped back after from his blistering start with a 73 but Peter Lawrie is five under after a solid 68. Damien McGrane was yet to finish his second round.