He chalked up nine birdies in a second-round 62 to take the clubhouse lead on 13 under par.
Sharing second place on 12 under were South Korean pair Baek Seuk-Hyun (63) and Yang Yong-Eun (63), the 2009 U.S. PGA Championship winner.
Swedish amateur Marcus Kinhult was in fourth spot on nine under after posting a 66.
"I hit it well on the range this morning, got into a nice rhythm early on and carried it through the whole round," Willett told reporters.
"Over these last two weeks I haven’t been getting too far ahead of myself and every time I’ve got in trouble I’ve just taken my medicine and moved on to the next hole."
American Patrick Reed (69) was in a group on four under par, one better than Britain's Lee Westwood (69).
Spaniard Sergio Garcia faces an anxious wait before he discovers on Saturday if his one-under-par aggregate will be good enough to make the cut.
Twelve groups were unable to complete their rounds before the storms engulfed the Swiss Alps.
(This story has been refiled to correct typo in intro)
(Writing by Tony Jimenez, editing by Ken Ferris)
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