Bogey team Glamorgan threw Surrey's hopes of qualifying for the Vitality Blast quarter-finals back into doubt after a scintillating run chase.

The Welsh side have never lost a T20 match at the Kia Oval – winning six with the other rained off - and ensured their own hopes of reaching the knockout stages were revived on Tuesday night as they won by four wickets with an over to spare.

Surrey would have gone top of the South Group had they successfully defended their seemingly formidable 194-4 only to suffer their first defeat in any format since July 6. Now they stand fifth in the table, four points behind leaders Kent and Gloucestershire.

It puts extra importance on Friday's clash with Middlesex at The Oval, which is followed by a trip to Chelmsford on Sunday to meet Essex, with games still to come involving Sussex (August 9, home), Somerset (Aug 10, Taunton), Gloucestershire (Aug 15, home) and then the return with Glamorgan in Cardiff on August 17.

A typically quickfire opening partnership of 54 in 5.4 overs between Jason Roy (27) and Aaron Finch (30) had given the hosts an ideal platform after choosing to bat first on a used pitch. Finch’s fellow Australian Nic Maddinson then showed why he is so highly rated in T20 cricket with an innovative 70 from 45 balls, which included five fours and three sixes, aided by Ben Foakes (27) before Ollie Pope’s 26no from 15 balls in the closing stages lifted Surrey to what appeared a defendable total.

That seemed all the more likely when Glamorgan were reduced to 15-2 in the third over, including Australian Test player Usman Khawaja for 10, particularly as they were missing skipper Colin Ingram (sick) and another Aussie in Joe Burns (injured).

But Craig Meschede’s 43 off just 19 balls showed there was plenty of fight in the Welsh side, hammering off-spinner Gareth Batty’s first three deliveries for sixes and adding 50 in four overs with youngster Kiran Carlson, whose 58 from 32 included five fours and four sixes.

Neither the experienced Batty nor leg-spinner Scott Borthwick, whose two overs disappeared for 33, could offer control for Dernbach, who should have brought himself back earlier and only delivered three of his overs. Graham Wagg, having smashed a double-century against Surrey in the County Championship three years ago, ensured the pace never relented to finish with 46no, which included three sixes.

“Hats off to the Glamorgan boys – they produced some serious ball-striking,” admitted Dernbach.

“At halfway we were pretty happy. Maddinson accelerated to what I thought was a defendable score.

“The ball skidded on a bit more under the lights but a couple of their guys struck the ball beautifully and made it look fairly easy. Every time Glamorgan come here they seem to enjoy playing at The Oval, so fair play to them.”

Surrey will be hoping to recapture the form which saw them annihilate Somerset last Friday, a match which was in considerable doubt because of persistent thunderstorms but finally went ahead – thanks to the fine work of the Oval groundstaff – as a 10-overs match.

When the visitors slumped to 46-5, Tom Curran and Rikki Clarke claiming two wickets apiece, it seemed a damp squib at best before captain Lewis Gregory intervened with 50 from 23 balls.

West Indian speedster Jerome Taylor’s nightmare first over for Somerset cost 20 to launch a ferocious reply, Roy (28) and Finch (43no) running amok to crunch 69 in the first 3.5 overs and tee up a win by nine wickets in 6.4 overs.