Brun was among the early starters at St Francis Links and carded seven birdies and two bogeys in a second round of 67 to set the clubhouse target on eight under par.
Sweden's Jens Dantorp compiled a superb 63 to reach seven under alongside England's Matthew Baldwin and South Africa's Albert Venter before play was halted shortly before 2pm local time.
No further play was possible and the second round will resume on Saturday.
Speaking about the contrasting conditions on Thursday afternoon and Friday morning, Brun said: "(It was) very different. It's the first time for me that I've seen the course without wind.
"It was definitely a lot more receptive and the greens were better as well so you could make more birdies and just have more fun out there. I'm looking forward to (the weekend).
"It's nice to be in contention and to have a chance but there's a long way to go obviously."