The Blitzbokke got off to a flawless start, with a 21-0 victory over the United States and a 43-0 thumping of Cook Islands.
Against their strongest challenger in Pool B, the South Africans hit back in the second half to secure a 14-10 win over England.
Trailing 5-0 at half-time, Mark Richards dotted down a minute after the break and Branco du Preez converted to give the Blitzbokke the lead.
Du Preez crossed the line midway through the second period, and converted his own try, to extend the gap.
Greg Barden scored in the dying stages, but a second missed conversion saw England settle for second place in the group.
Last year's IRB Sevens Player of the Year, Cecil Afrika, scored a brace against the US and another try against Cook Islands, but was rested with regular captain Kyle Brown for the game against England.
South Africa's coach, Paul Treu, said he was pleased with the team's overall performance.
"We started a bit slow against the US, got our into our rhythm against the Cook Islands and played a good structured match against a strong England side," Treu said.
"While I'm happy that we managed to win all three of our pool matches, we all know that what really counts is how well you play on day two.
"Cecil and Kyle each played two hard matches and we thought it would be in the best interest of the team to rest them against England."
South Africa, lying third in the series standings after the first three legs, face log leaders Fiji in the cup quarter-finals on Saturday.
Treu said his team would focus on achieving their own targets on day two.
"We have our goals and will focus on those instead of other things," he said.
"Hopefully we will be able to keep the momentum from the start on Saturday."