Lagergren is chasing a first win on the DP World Tour since 2018 at the Gary Player-designed 8,233-yard course, which holds the record for being the longest on the tour.
He started his round on the 10th hole and carded four birdies in his first nine, before picking up a further three after the turn to finish one shot ahead of South Africa’s Casey Jarvis (66).
Jarvis, who also carded seven birdies but had a bogey on the par-four 16th, was the early leader in the clubhouse before Lagergren overtook him late in the day.
Jarvis admits the length of the course makes it a big challenge for those who aren't as explosive off the tee.
"I played really nicely and I’m happy where my game is at. It is a long course so I tried to step on a few drives out there," Jarvis said.
"I don’t hit the ball as far as some of the other guys out here and it is a long walk, so it is a bit mentally challenging. You just have to stay patient."
There are a trio of players two shots behind Lagergren, including England’s Andy Sullivan and home golfers Javan Rebula and Louis de Jager, who all carded 67s.
