Guerrier, who claimed a maiden DP World Tour title in Andalusia in October, sank eight birdies but also carded four bogies as all players found the back nine in particular a challenge in the second round.
Defending champion Max Homa (75) from the United States looked set to top the leaderboard until he suffered consecutive double-bogeys on the par-three 16th hole and the par-four 17th. He is in tied fourth on three-under-par for the tournament.
Home golfer Ockie Strydom (73) was also in a strong position going into the back nine, but a double-bogey on the par-four 13th and further dropped shots on 15 and 17 dropped him back to four-under-par, one shot behind Guerrier.
Another Frenchman, Romain Langasque, is also a shot behind compatriot Guerrier after he carded a 70 on Friday. He might have had a share of the lead but bogeyed the par-four 18th.