Guerrier, who is on 12 under par, will rue not being further ahead after he bogeyed the first and last holes at the Southport links.
Elsewhere, midway leader Paul Waring, who's sitting on 11 under, is embroiled in a close three-way tie for second place with Scotland's Richie Ramsay and Jens Dantorp of Sweden.
An enthralling final day of action is expected, considering ten other players are still within four shots of Guerrier ahead of Sunday.
One man hoping to mount a serious challenge in the fourth and final round is Scotland's Ramsey.
The 39-year-old is now sensing an opportunity to make amends for his near miss at the British Masters at The Belfry in May, when he surrendered at least a play-off place with a double bogey on the last.
Ramsay said on Sky Sports: "It's not something that's easy to get over but, when I look back on it now, I think to myself 99% of what I did that day was really good.
"Maybe one per cent cost me but I put myself in a position. It was just one shot, a fraction of the overall work that you've done. I've got to take that into consideration and think positively about it.
"I made a promise to my daughter a few years ago that I'd get her a trophy. I like to keep my promises, especially to her.
"To win tomorrow would be brilliant but it's trying to put that out of my mind and just thinking about just what am I doing on the next shot."