England blew another lead and fell to a fifth straight Test defeat as the Springboks won the series with a game to spare in a 23-12 victory in Bloemfontein.
Eddie Jones' side took a 12-0 lead inside 12 minutes but failed to push on and for the second time in two weeks, allowed the hosts back into the game.
South Africa had the better of the starts and only an Owen Farrell tap tackle prevented Damian de Allende from running the length of the field having intercepted a pass from Ben Youngs. But England survived and they owed their pack a huge debt after conceding a scrum five metres from their own line but they won the penalty and cleared their lines.
And after holding firm in defence, Eddie Jones' backline burst into action, with two tries in two minutes 10 minutes in. Youngs found Henry Slade and as Farrell received the ball he drew right wing Sibusiso Nkosi before finding May. With the Leicester Tigers winger drawing Willie Le Roux, it left Mike Brown with the easiest of opportunities to score.
Farrell added the extras and minutes later Brown became provider as he juggled the ball before flicking the ball on to Elliot Daly who fed May who ran in to score in the right corner.
The Springboks sprang into life but despite winning penalties off the back of their powerful driving maul, they coughed up possession when they edged towards the line.
But with the writing on the wall for some time, the staunch England defence finally succumbed to the South African attack after a break from Tendai Mtawarira, When the front row was finally put to ground, backrow Duane Vermeulen took up the charge in the 22 and touched down after beating three English defenders.
Handre Pollard added the conversion and two penalties to give the Boks a 13-12 half-time lead.
Rassie Erasmus' side came out with ambition and were rewarded eight minutes after the restart and having gone for the scrum from a penalty, referee Romain Pooite awarded a penalty try as the series drifted away from England.
Their was Brad Shields came within inches of touching down in his first start, 16 minutes into the second half but Franco Mostert got back to knock the ball from the lock's hands. With a penalty advantage, England came back for the scrum, but a massive defensive effort from the Boks' pack won the resulting scrum.
Pollard added two penalties to seal the victory, which leaves Eddie Jones with a fifth straight Test defeat and a sixth straight defeat as he goes into the final game of the series next week.