The former Masters champion enjoyed back-to-back victories at the Royal Johannesburg and Kensington Golf Club in 2010 and 2011 but Sterne also has two to his name, in 2008 and 2013.
Both are in the field this week and after playing just one competitive tournament this year Schwartzel is ready for his return.
"After some time off I always feel fresh because I drain more mentally than I do physically," he said.
"It's nice to have had time off and I feel up for the challenge and in our game that's 85 per cent of the battle won.
"Time will tell what's going to happen, but at least I feel good.
"We (he and Sterne) have played a lot of good golf around here so we're pretty comfortable with it and I don't think anything really changes for me around here.
"It's always good to play in this tournament at a course that I like, and it's no different this year."
South Africans have won five of the last seven editions but Schwartzel is not underestimating the threat of the international challenge.
"It's not nice when they come and beat you on your home soil," he added on europeantour.com.
"There are a few guys out here that can play it well.
"Alvaro Quiros is here and he is one of the longest hitters in the game so if he hits it straight then he'll have a good chance this week."
Defending champion Sterne insists he is not the one under more pressure.
"It would be nice to defend and win three times but it doesn't put any pressure on me or anything," he said.
"I'll just take it as it comes and hopefully come Sunday I've got a chance.
"We've got a couple of good players here this year so it's going to be a bit stronger field.
"I feel like I'm playing well and I just have to cut out the mistakes and then I should be up there again."
Aside from the £171,000 first prize there are three spots on offer at this year's Open at Royal Liverpool as the Joburg Open is the second event in the qualifying series.
Three players, not already exempt, who finish in the top 10 and ties will secure a place for the 143rd Open Championship at Hoylake in July.