Somerset's Clydesdale Bank 40 specialists set them up for a sixth straight win in the competition as they thrashed Surrey by 94 runs.

Zander de Bruyn and James Hildreth smashed 145 in 19 overs to set up a total of 303-5 – a record score in matches between the sides at the Oval.

The pair – with 308 and 338 runs respectively – are by some distance the club's top scorers in the 40-over competition. They galvanised a Somerset innings that could have faltered at 124-3 following Marcus Trescothick's opening 69 after the visitors won the toss.

South African de Bruyn rarely grabs the headlines but his consistent contributions have helped Somerset become one of the premier teams in English one-day cricket.

Yesterday, he hit seven fours and Somerset's only two sixes as he reached 89 from 78 balls.

Hildreth's 68 from 55 deliveries helped erase another record – the 120 he and Ian Blackwell put on at the Oval in the totesport League in 2005, previously Somerset's best fourth-wicket stand against the Londoners.

Hildreth and de Bruyn are a potent combination in the middle of a one-day innings – they accumulate well against spin because both are expert exponents of the sweep and the reverse-sweep.

De Bruyn benefited from being dropped by England Lions wicketkeeper Steve Davies on 12 off Gareth Batty's off-breaks. But otherwise the duo tucked in against the slow men and then gorged themselves on the pace of Jade Dernbach, whose figures had already been wounded by Trescothick. The youngster bowled the seventh over and Trescothick struck each of his first five balls for four. The next was a wide and the skipper then took a single to keep the strike before clobbering Chris Tremlett for four, four and two to realise 32 in the space of nine deliveries.

Fellow opener Craig Kieswetter's tough run of form continued as he holed out to long-on, Trescothick, who has now gone 37 innings without a hundred, swept to deep backward square leg and Nick Compton was stumped off a leg-side wide.

The last nine overs of the innings went for 102 runs – thanks to the power-play.

Somerset had selected a side with one fewer specialist bowler than usual, but they were never in danger. Openers Rory Hamilton-Brown and Davies both picked out mid-off to give Alfonso Thomas and Pete Trego wickets during the fielding restrictions.

Jason Roy pulled de Bruyn to Jos Buttler at square leg after he and Mark Ramprakash had added 40 in six overs.

Ramprakash scored 42 before he became the first of two wickets in as many deliveries for Murali Kartik. The Indian left-arm spinner has agreed to re-sign for Somerset for 2011 and he had the veteran caught at long-on before Stewart Walters edged the next ball and Kieswetter held on well.

Chris Schofield survived the hat-trick ball but there was no way back from 110-5 – even with the floodlights on to negate the heavy cloud cover in the capital. Kartik had Schofield leg before wicket on his way to the best figures of the match – 3-40.

Trego had a second wicket when Batty skied to deep cover before top-scorer Matt Spriegel miscued Mark Turner to long-off for 53 as Surrey were 209 all out.