Surrey 265 for 8 (Ansari 66*) beat Yorkshire 259 for 7 (Ballance 77, Maxwell 55, Ansari 3-58) by six runs
Gary Ballance hit his second fifty in three days after being dropped by England but it was not enough to prevent Yorkshire from losing to Surrey by six runs in the Royal London Cup at the Kia Oval.
Ballance survived an early drop by Gareth Batty when on 3 and looked like making Surrey pay when he got to 77, helping Yorkshire close in on a target of 266. But he then swept Zafar Ansari straight to deep square leg and the task of scoring 22 off the last 16 balls proved beyond the Yorkshire tail.
Surrey had set them a challenging target thanks to an eighth-wicket stand of 66 in seven overs between Ansari, who finished unbeaten on 66, and Tom Curran, who made 44.
Steve Davies had given Surrey a flying start with 39 off 32 balls but the innings almost stalled against some tight bowling from Steven Patterson, Yorkshire's most dependable seamer, and Karl Carver, a 19-year-old left arm spinner making his List A debut.
Patterson bowled Davies with his seventh ball and had a frustrated Jason Roy, who had made two centuries in his last three innings, caught at midwicket. Carver had Gary Wilson caught at mid-off and Kumar Sangakkara, who had struggled to 23 off 45 balls in his 506th List A innings, taken at square leg.
Ben Foakes gave the innings some momentum with 44 off 52 balls but when he and Batty were both caught at mid-on off Glenn Maxwell and James Burke was caught and bowled by Matthew Fisher, Surrey were still labouring at 187 for seven.
It was then that Tom Curran launched his assault. He made his intentions clear by driving Maxwell over long-off for the first six of the match and when the offspinner was kept on for what turned out to be an over too many he struck him for 4, 6, 4 off successive balls.
When launching their reply, Yorkshire soon lost Andrew Gale, lbw to the impressive 17-year-old Sam Curran, but Alex Lees and Maxwell gave them a solid foundation with a second wicket partnership of 67.
Lees made 28 and Maxwell 55, his second highest score for Yorkshire, and it looked as though Yorkshire would coast to victory when Ballance was sharing stands of 65 with Jack Leaning and 41 with Andrew Hodd.