Surrey 165 for 5 (Amla 55, O'Brien 40) beat Glamorgan 148 for 8 (Allenby 52, Curran 3-23) by 17 runs
After being put in to bat Surrey made 165 for 5 from their 20 overs, but despite a half-century from captain Jim Allenby Glamorgan, not helped that Darren Sammy was out first ball, could only reach 148 for 8. The win saw Surrey leapfrog Glamorgan into third place.
Surrey had got off to a reasonable start with 10 runs coming off Graham Wagg's first-ball no-ball - which Amla dispatched to the ropes before repeating the trick with the extra delivery.
Amla was dropped at extra cover on 42 in the 11th over after Surrey had reached 74 for 2 at the halfway stage. Surrey then lost captain Gary Wilson, who was caught at long-off off Dean Cosker to leave the visitors 85 for 3 in the 12th over.
The Surrey 100 came up with the first six of the innings struck by O'Brien off Cosker, who still managed useful figures of 2 for 25 from four overs. Amla brought up his 50 in the 14th over off 42 balls but in the next over was caught at the second attempt by his countryman Jacques Rudolph at short fine-leg off Wagg with Surrey 110 for 4.
Sammy bowled a mixed 18th over, with two no-balls before removing Azhar Mahmood. Surrey managed to score 48 off the final four overs helped with a second six for O'Brien.
Glamorgan suffered an immediate setback when Rudolph was dismissed with the second ball of the innings, caught behind attempting to cut Jade Dernbach.
Mark Wallace gave Glamorgan a boost with a sweep for six off Mahmood but in the next over he was caught off Tom Curran at third man. After the Powerplay, Glamorgan had reached 44 for 2.
Captain Allenby gave the Glamorgan innings some much-needed impetus, slog-sweeping Gareth Batty's first ball for six. He followed that with a six off Curran over midwicket as 14 came off the ninth over.
After Batty bowled five wides, Allenby reached 50 off 38 balls as Glamorgan reached the halfway stage at 80 for two.
Glamorgan's hopes were hit when Allenby was stumped off Batty for 52 from 42 balls, leaving the home side on 90 for three in the 12th over. Curran came back into the attack and had Chris Cooke caught at long on and then bowled Ben Wright around his legs.
It brought Sammy to the middle with 55 runs needed from five overs, but he was trapped lbw first ball to Robin Peterson. It got down to Glamorgan needing 37 off the final 18 balls, but Glamorgan's chances went when Wagg and Stewart Walters were out in the space of five balls.