Surrey 168 for 5 (Stoneman 73*, Pillan's 4-57) beat Yorkshire 165 (Atkinson 4-43) by five wickets
Gus Atkinson's four-wicket List A debut helped Surrey make a winning start to their Royal London Cup campaign as they eased past Yorkshire by five wickets at Scarborough.
Atkinson, 23, prospered with the new ball on a fast and bouncy North Marine Road pitch, claiming 4 for 43 to bowl the Vikings out for 165 in only 35 overs.
Hashim Amla elected to bowl at the start of this Group B fixture, and the South African batting great later went beyond 10,000 career runs in this format with 29 to begin a successful chase. But Mark Stoneman played the match-clinching innings, an unbeaten 73 off 110 balls, having only just returned to Surrey following a four-game T20 loan spell with Yorkshire.
Stoneman and co survived 4 for 57 for South African overseas quick Mat Pillans, who moved from Surrey to Yorkshire in late 2018.
This fixture included eight players - four on each side - making their List A debuts.
Atkinson made the initial breakthrough by bowling Will Fraine in the second over before getting George Hill caught at square leg and Jonny Tattersall caught behind as the hosts slipped to 40 for 4 in the 10th.
Matthew Revis, another List A debutant, top-scored for Yorkshire with 43 off as many balls, while Gary Ballance made 39. They shared 81 inside 13 overs for the fifth wicket. But wickets fell quickly once more.
The Vikings tumbled from 121 for 4 in the 22nd, losing their last six for 44 as most of the damage was done from the Trafalgar Square End.
Opener Harry Duke, Hill, Ballance and Pillans were all undone by extra bounce, while Revis and Dom Bess will reflect on loose dismissals.
This certainly wasn't the way Yorkshire captain Bess would have wanted to celebrate his 24th birthday, with him skewing Dan Moriarty's left-arm spin to long-off.
Hill and Pillans fell caught off top-edged pulls against Atkinson, the latter courtesy of a stunning diving catch on the run towards backward square-leg from wicketkeeper Jamie Smith. Ballance fended a short ball from Conor McKerr to gully, sparking the clatter of wickets.
Amla and opening partner Stoneman then steadily shared 59 inside the first 13 overs of the chase. Stoneman hit two fours and slog-swept Bess for six as 14 came off the 12th, only for Pillans to claim two wickets in three balls in the 13th. He had Amla caught at wide mid-on pulling before bowling Ben Geddes, leaving Surrey 59 for 2.
That forced Stoneman back into his shell, but he shared an important 54 with Smith. Pillans then struck twice in an over again, getting Smith caught at midwicket for 25 and Ryan Patel superbly caught one-handed in the gully by Tattersall - 116 for 4 in the 29th.
Bess also bowled debutant Nico Reifer for an eye-catching 26, but Surrey's victory was secured with 10.5 overs remaining.