Joe Root's eighth one-day century was in vain as South Africa beat England by one wicket to level the ODI series 2-2.
The Yorkshire batsman scored 109 off 124 balls as England recovered from 108-6 to post 262 all out.
England looked to be heading for victory when they reduced South Africa to 143-5, with AB de Villiers brilliantly run out by Chris Woakes.
But Chris Morris hit a superb 62 from 38 balls as South Africa reached the target with 16 balls to spare.
Morris was bowled with the penultimate ball of the match to set up a dramatic finish, but Imran Tahir - who had earlier starred with three wickets - hit Adil Rashid for four to seal victory.
England must now beat South Africa in Cape Town on Sunday to clinch their third win in four ODI series.
It was an extraordinary, perhaps career-defining knock from 28-year-old Morris, who came in at number eight with a highest score of just 12 to his name from nine previous ODIs.
Last week Morris was bought for 70 million rupees (£707,882, or $1,027,607) by the Delhi Daredevils at the Indian Premier League auction and he underlined his considerable value in limited-overs cricket here with a breathtaking exhibition of clean ball-striking.
Having been dropped by Rashid on 14, the million-dollar man cashed in, bludgeoning four sixes into the thin highveldt air to guide his team to the brink of victory before Rashid finally removed him with a googly.
It was a masterclass in seizing the initiative, with South Africa having looked second favourites for much of the chase.
Stuart Broad removed Hashim Amla in the first over and Ben Stokes bowled the in-form Quinton de Kock before Woakes - dropped for England's World Twenty20 squad - proved a point with the wicket of Faf du Plessis and the run-out of the talismanic De Villiers.
Farhaan Behardien and David Wiese briefly stemmed England's momentum with a partnership of 48, but when they were out in quick succession, followed by Kagiso Rabada to leave the hosts 210-8, an England series win looked inevitable.
The series so far
1st ODI (Bloemfontein): England won by 39 runs (D/L)
2nd ODI (Port Elizabeth): England won by five wickets
3rd ODI (Centurion): South Africa won by seven wickets
31.49°C Kathmandu
