Cape Town - AB de Villiers' 64 from 45 and Imran Tahir's 3/17 could not save the Proteas from defeat in the third T20I against Sri Lanka at Newlands on Wednesday.
De Villiers, Reeza Hendricks (41 off 33) and Mangaliso Mosehle (32* off 15) had helped guide the hosts to 169/5 from their 20 overs, but Sri Lanka got to the total with a ball to spare to win by 5 wickets after an intense and dramatic run chase.
The win gives the Sri Lankans a 2-1 series triumph and their first trophy of any kind in South Africa.
South Africa did not do themselves any favours in the field, dropping at least six catches.
The momentum ebbed and flowed between the visitors and hosts, but in the end poor fielding from the South Africans proved the difference.
The Sri Lankan run chase got off to a threatening start through Upul Tharanga and Niroshan Dickwella as the pair raced to 36/0 in four overs before Wayne Parnell removed Tharanga (20) with his first ball of the innings.
Then, as he has done so many times before, Imran Tahir struck immediately when he bowled Sri Lankan captain Dinesh Chandimal (5) and South Africa began to wrestle back the momentum.
Parnell could have had another in his second over, but three dropped catches in three balls remarkably left him empty-handed.
Dane Paterson dropped a sitter at fine leg to put down Dhananjaya de Silva, Mosehle got a glove on a top edge from Dickwella before Parnell put down Dickwella off his own bowling.
Before that, Lungi Ngidi had put down a tough chance off Paterson and Tahir had dropped a very easy chance off Parnell as the Proteas let themselves down in the field.
It just wasn't happening for the Proteas, with balls either being dropped or falling short, and when Dickwella got to 50 off 34 balls in the 12th over, Sri Lanka began to emerge as favourites in the clash.
To make matters worse, Ngidi was forced off the field with what seemed like a hip injury after he had bowled just two overs.
Behardien had saved Tahir one over for the business end, and it seemed to be a masterstroke when South Africa's leggy had the dangerous Dickwella (68 off 51) caught by the Proteas skipper on the deep mid-wicket fence.
Tahir then had his third when De Silva (19 off 27) came dancing down the wicket only to miss and be stumped by Mosehle.
Those two blows, all of a sudden, gave the Proteas the edge.
Tahir finished with 3/18 from his four overs in a spell that looked to have won his side the game.
But Sri Lanka weren't done, and an over that went for 19 off Parnell swung it back their way.
The visitors went into the last three overs needing 33 for victory, and the ball was given to Paterson on debut.
The Cobras seamer ran out Kusal Mendis after gathering off his own bowling, but the new danger man was Seekkuge Prasanna at the other end.
Prasanna hit Phehlukwayo for 15 off the second to last over, and Paterson was asked to bowl the last over with Sri Lanka needing 11 for victory.
They did it with a ball to spare as Prasanna (37* off 16) was the unlikely hero.
Earlier, De Villiers took a while to get going - he was 29* off 25 balls - but he soon found his rhythm and went on to blast three sixes in a knock that is good news for South Africa in an ICC Champions Trophy year.