Glamorgan 181 for 6 (Donald 76, Ingram 42 ) beat Surrey 175 for 7 ( T Curran 51*, Stoneman 34, Finch 33, de Lange 3-29) by six runs
Aneurin Donald's brilliant 76 off 40 balls shone out under the Kia Oval floodlights as Glamorgan strengthened their position at the top of the NatWest T20 Blast's South Group table by squeezing past Surrey by six runs in front of a crowd of 21,256.
But Tom Curran almost stole the match for Surrey at the death, his remarkable 51 not out from 27 balls making a mockery of 48 runs being required from the last three overs to overhaul Glamorgan's 181 for 6. In the end, having hit the second ball of Michael Hogan's final over for six to bring the equation down to nine from four balls, Curran was foxed by two slower balls from the veteran Australian seamer which he swung at and missed.
A scampered two from the penultimate ball left Curran, who hit three sixes and three fours, needing seven from the last ball. He hit it into the offside, opted not to run but still walked off to an ovation for a courageous attempt to achieve the seemingly impossible with Surrey finishing on 175 for 7.
Donald, still only 20, hit two sixes and 11 fours in his T20-best as he and the prolific Colin Ingram, who scored 42 from 31 balls with three sixes, swept Glamorgan towards their eventual total by adding 95 in just 8.3 overs for the second wicket after they had opted to bat first.
It was Glamorgan's fifth win of the group stage and took them to 14 points while Surrey, who have now lost four of their ten games, remain on 10 points.
Glamorgan captain Jacques Rudolph praised Donald's batting plus Michael Hogan's nerve in the thrilling final over.
"Tom Curran did incredibly well to get them so close, and there is so much noise out there in front of a crowd of that size that it's difficult to communicate," he said. "But Michael kept his cool after the second ball six and showed his experience to switch to around the wicket and bowl two vital dot balls. It was a brave decision.
"Aneurin batted brilliantly up front and it was a pretty solid batting performance although we might have got 20 runs more after the start we got."
Surrey's chase did not start well, with Jason Roy nicking the first ball of the innings, from Lukas Carey, to the keeper but Mark Stoneman joined Aaron Finch in a stand of 64 in six overs before carving to deep midwicket in Graham Wagg's first over to go for a useful 21-ball 34.
Finch, who had got off the mark by swinging Michael Hogan for six from his first ball, and who also hit Marchant de Lange for six, reached 33 from 22 balls before mishitting Ingram's occasional legspin straight to long on in the eighth over, and Surrey's decline continued as Moises Henriques and Sam Curran were both held in the deep.
From 84 for 3 after ten overs, Surrey slid to 101 for 6 as Rikki Clarke could only score 6 on his Surrey return before becoming one of de Lange's three victims.
Ollie Pope, caught at midwicket off de Lange, scored a sparkling 26 and Surrey's hopes rose further when Tom Curran swung Hogan for six in an 18th over costing 16 runs and also containing fours by both Curran and Stuart Meaker.
That left 32 needed from the last two overs, and Curran immediately swatted Graham Wagg's left arm seam over wide midwicket for six. Riding his luck, with an inside-edged four to fine leg, Curran ensured that 15 came from the over - setting up the superb finish.
When Glamorgan batted, Donald was quickly into his stride, pulling for six the fourth ball of the innings from Jade Dernbach - and the second ball he faced - before taking three fours from Sam Curran's opening over with a lovely straight drive, a paddle-pull to wide long leg and then a crashing drive through extra cover.
Another flipped four, off Dernbach, followed before the wicket of Jacques Rudolph slowed Glamorgan for a while. From 30 for no wicket after three overs, they could only score 46 for 1 from the initial six-over Powerplay after Roy leapt to take a brilliant catch at backward point to send back Rudolph for 4.
The bowler was Clarke, who has rejoined his first county Surrey, for whom he played from 2002 to 2007. Initially, the move is on loan from Warwickshire ahead of a permanent move from next season, with Dom Sibley already going the other way in a reciprocal deal, and 35-year-old allrounder Clarke struck with his fifth ball in the fourth over. His first two overs cost only eight runs and he finished with 1 for 23.
Ingram, however, still managed to hit his first ball, from Clarke, for four and he was soon pulling Tom Curran for four and launching Gareth Batty's offspin for six in the eighth over. Another six arrived when Ingram pulled the younger Curran out of the ground beyond the Peter May Stand as the Welsh county reached the halfway mark at 87 for 1.
Batty was then plundered for 22 in an over by Donald, with three leg-side fours and a smeared six being followed by a delicate lap for four by the youngster from the last ball of the 11th over.
A four and straight six by Ingram off Henriques's medium pace quickly followed but the rollicking second wicket stand ended in the 13th over when Donald skied paceman Meaker to midwicket.
Ingram went six balls later, cutting Henriques to point, and three more wickets fell in the final overs as Glamorgan's middle-order sought to add as many as they could. David Miller's 24 from 19 balls included a last over six off a Tom Curran full toss the ball before he fell attempting to clear long-on, while Wagg also swung Clarke for six.