South African duo Martin Maritz and Tyrone Mordt fired bogey-free 9-under rounds of 62 to share the first-round lead at the Joburg Open yesterday.

Both players had nine birdies to top the leaderboard by one shot at the $1.7 million event, the last — and richest — of the four tournaments in South Africa to open the European Tour’s 2011 Race to Dubai.

Another South African, Branden Grace, was one shot back after six birdies and an eagle for his 63. Thomas Aiken and Frenchman Alexandre Kaleka were tied for fourth on 7 under.

Maritz’s faultless performance on the longer, tougher East Course at Royal Johannesburg was the round of the day.

The 33-year-old Maritz, who gave up full-time tour golf three years ago to become a club pro in the United States, picked up shots at his first two holes and then had four consecutive birdies from No. 13 to top the leaderboard alongside Mordt — who opened on the shorter West Course.

Players alternate courses over the first two days at the Joburg Open, which was co-sanctioned by the Sunshine Tour, with the final two rounds played on the championship East Course. Both courses are par-71s.