Gloucestershire 301 (Bancroft 100, Hammond 51, McKerr 4-32, Steel 4-61) beat Surrey 264 (Patel 87, Blake 50, Taylor 4-44) by 37 runs
Cameron Bancroft's 100 from 109 balls was backed up by an excellent bowling effort as Gloucestershire opened their Metro Bank One-Day Cup account with a convincing 37-run victory against Surrey at the Kia Oval.
A defiant 87 from 96 balls by Ryan Patel, and 50 off 45 from Josh Blake, could not prevent Surrey from reaching only 264 in reply to Gloucestershire's 301 all out, in which Miles Hammond had also made 51 and skipper Jack Taylor an explosive 44 with five sixes.
Fast bowler Conor McKerr impressed for Surrey with List A best figures of four for 32, while Cameron Steel finished with four for 61, but overall Gloucestershire's attack was more consistent with pacemen Matt Taylor and Ajeet Singh Dale both outstanding.
Both teams were winless after their first two games, but it is Surrey who remain marooned at the bottom of the Group B table. For Gloucestershire, left-armer Taylor took four for 44 and Singh Dale two for 49.
Blake and McKerr, who made 37 from 35 balls, hit out bravely in a seventh-wicket stand of 85 in 12 overs after Patel and Ben Foakes had rallied Surrey from 51 for three with a partnership worth 89.
Taylor, who had removed both Dom Sibley, leg-before for nought, and Ben Geddes (14) in a superb five-over new ball burst of two for 10, later produced a sharp lifter that McKerr could only fend off to keeper James Bracey.
Singh Dale had earlier returned for a second spell to have Foakes caught at deep square leg for 34 and then opener Patel - who had struck three sixes and seven fours - held by Bracey, thick edging as he tried to force away a short rising delivery to leave Surrey 153 for six.
Rory Burns had fallen earlier for just six, leg-before to Ollie Price's off spin, and after Price and left-arm spinner Tom Smith had combined effectively in mid-innings to peg back Surrey's scoring rate it was another slow left-armer, Graeme van Buuren, who had Steel caught behind for a duck in between the Foakes and Patel dismissals.
That left Blake and McKerr, who both hit sixes off Matt Taylor, to keep Gloucestershire waiting for a deserved victory and when Dom Goodman sprinted 20 yards towards mid off to claim a Blake skier off his own bowling it was all but over.
Bancroft's fifth List A hundred perfectly anchored Gloucestershire's innings, while his fellow opener Hammond's 57-ball half-century provided initial forward momentum and Jack Taylor's 26-ball cameo gave the visitors late acceleration.
Surrey, however, would still have been happy enough to limit Gloucestershire to 301 after they had reached the 40-over mark on 248 for four and with Taylor already beginning to hit out strongly in a 56-run stand with Bancroft.
Steel picked up his fourth wicket by having Bancroft leg-before, sweeping, and McKerr almost immediately had Van Buuren caught at the wicket for a duck with a fine leg-cutter to peg the visitors to 260 for six.
Taylor had by then square cut returning paceman Nathan Barnwell over the third man ropes for his first six, as well as slog-sweeping Yousef Majid's left arm spin into the stands, but soon he struck James Taylor's fast-medium for successive legside sixes before the same bowler ended his assault with the last ball of the 45th over.
And suddenly, with McKerr on a hat-trick after removing Smith (3) and Goodman, from an edge behind to a diving Blake and then a mis-cued swat to mid wicket, Gloucestershire were 289 for nine.
McKerr's hat-trick ball then almost found the edge of last man Singh Dale's bat as it whistled through to keeper Blake, but Sibley dropped Matt Taylor at long on off Steel, leaving him to finish unbeaten on 19 when Singh Dale fell to McKerr for six.
Earlier, Hammond had dominated a first wicket stand of 79, after Gloucestershire had been put in, hitting two legside sixes and five fours.
Majid saw Hammond chip the last ball of the 15th over straight to mid wicket but was then swept for six by Bancroft as the Australian international was joined by Price in a second wicket stand worth 74.
Price was smartly stumped by Blake on 32, missing a cut when advancing to Steel, and the leg spinner had the last laugh after Bracey skied to long on after slog-sweeping him over the mid wicket ropes to go to 16.
Steel's googly bamboozled Ben Charlesworth on 12, the left-hander thin-edging to Blake, but Taylor arrived to help Bancroft push Gloucestershire's total on to challenging proportions - and one which proved beyond Surrey.