Somerset 283 (Trego 65, Gregory 56, van der Merwe 52, Finn 4-65, Patel 3-48) beat Middlesex 230 (Simpson 77, van Meekeren 3-32) by 53 runs
After back-to-back defeats against Sussex and Essex, Somerset proved too strong for a Middlesex side for whom this was a second defeat of the 50-over season.
Trego weighed in with 65 and a wicket whilst Gregory helped himself to an equally valuable half century and a brace of wickets, as Somerset won by 53 runs. Van der Merwe finished with a wicket too having struck 52 in a match-winning 91-run partnership with Gregory.
Having been asked to bat first, the host county lost their first two wickets inside the opening half a dozen overs as Steven Davies and Johann Myburgh were caught at the wicket off the bowling of Steven Finn.
Myburgh's departure brought James Hildreth to the crease, alongside the hard-hitting Trego. The pair batted sensibly for 10 overs before the in-form Hildreth, was needlessly run out, by Nathan Sowter.
Trego played well thereafter and with Matt Renshaw, added 50 in the next 10 overs. Renshaw, who has enjoyed a decent start to life in the west country, had looked in decent touch when he was stumped by John Simpson off the bowling of Ravi Patel for 24.
Six runs later, Tom Banton departed in similar fashion as Simpson bagged his fourth scalp of the innings. Patel bowled particularly well from the River End and shortly after, picked up the prize wicket of Trego at 159 for 6. Trego, having reached 50 off 60 balls with three fours, gifted Patel the most simple of return catches.
It required a partnership of note to guide Somerset away from any further trouble. And it came in the shape of Gregory and van der Merwe. The pair added 91 for the seventh wicket before the former, having struck one four and four sixes in passing 50 off 42 balls, was caught by Paul Stirling off the bowling of Tom Helm, for 56.
Van der Merwe, whose half century came off 44 balls, followed at 265 for 8, for 52, before Middlesex wrapped up the Somerset innings at 283 with Finn finishing with 4 for 65 and Patel 3 for 48.
The visitors' reply was far from smooth as Somerset bowled themselves into a position of relative strength. Gregory had Nick Gubbins caught by Hildreth at slip before Stevie Eskinazi was snapped up by the tumbling Steve Davies, without scoring.
When Hildreth leapt high to his left to catch Eoin Morgan at 39 for 3, Somerset sensed their under par score, with the bat, might just be enough.
Hilton Cartwright fell 27 runs later, for 4, to the most exquisite Banton catch at short cover, leaving opener Stirling to not only steady the ship but to lead the side towards their target.
Having batted well for 39, Stirling too departed to a catch behind the wicket. Davies, this time, took a regulation catch off the bowling of Paul van Meekeren off the first ball of the 18th over.
James Franklin fell to Jamie Overton to compound the problems and although Simpson led a mini revival, the early damage had taken its toll.
The wicketkeeper batsman shared in 44-run stands with Sowter for the seventh wicket and Finn for the ninth, before he and Patel had Somerset, looking over their shoulders.
In the end there was too much to do and Simpson was last man out for 77 with Middlesex 54 runs short of their target.