Former Masters champion Schwartzel has yet to record a bogey in the tournament so far and six birdies and an eagle on the par-five 18th hole catapulted him into a strong position at 13 under with Bourdy.
"I got off to a great start this morning. The golf course was in great shape, the greens were nice and there was no wind," he told reporters.
"It was there for the taking and luckily enough I took advantage early on. I made a couple around the turn and could have been a few more there, but we can't get too greedy."
Despite posting the lowest round of the tournament, the 28-year-old said he felt his form was still well below his best which may be an ominous sign for Bourdy and the rest of the field.
"When you're hitting it well you feel in control. The way I'm hitting it now it feels like I've got to dig a lot deeper to grind a score out," he said.
"It's not as consistent as it normally is. I just hope to start striking it better and feel a bit more at ease when I'm out there. Early on it wasn't that great, but it feels like it's getting a little better. Hopefully if I can take that and continue with it tomorrow then it will get better as the week goes on."
The afternoon field failed to make inroads on the leaders and it was Bourdy who once again shared the headlines as he backed up his opening score of 66 with another fine round that also included six birdies and an eagle.
"I'm not expecting, but you never know. I'm feeling great and I played two good rounds," he said.
"I had many birdie opportunities again today, especially on the first holes. My game was again solid, and I made just one bogey today, so it was a great round again.
"It's tough all week - you have to do the job over four rounds and that is difficult. When you play well you have to see how you are on Sunday. Tomorrow I will try to do the same - shot by shot, play my game. I think the top players will do the same."
As the two leaders pulled away from the chasing pack, only Fichardt could get within four shots as a tidy round of 68 edged him up to nine-under.
Rounds of 69 in the afternooon for Louis de Jager and England's Steve Webster got them to eight-under and a share of fourth, but the chasing pack will have it all to do if they are to catch the co-leaders at the weekend.
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