Bourdy, with three birdies on each nine Thursday, is one stroke ahead of a group of six players that includes South Africans Oliver Bekker, Louis de Jager, Darren Fichardt and Charl Schwartzel along with English players Richard Bland and Steve Webster.
Four more players are at 4-under and nine others are at 3-under 69, leaving 20 players within three strokes of the lead after Thursday's play.
Bourdy opened the tournament with a birdie at the first hole and posted back-to-back birdies at Nos. 5 and 6. He added two more birdies at 11 and 12 and took the lead with a 20-foot birdie putt at the par-3, 208-yard 16th hole. Bourdy was 3-under on pars 3s on the day.
Five of the six players tied for second also went without a bogey in the first round. De Jager had a bogey at the par-3 12th but also had a string of three consecutive birdies over Nos. 6-8.