Steven Davies hit 127 not out as Surrey made a mockery of a 229 target to beat Yorkshire Bank 40 holders Hampshire by nine wickets at The Oval.
Davies and his skipper Graeme Smith launched Surrey's run chase with an opening stand of 162 in 20.3 overs.
Hampshire spinner Liam Dawson (1-42) opened the bowling and eventually had Smith caught by James Vince for 74 but Davies and Vikram Solanki (22no) completed the job in 31.2 overs amid a flurry of pleasing strokes.
Wicketkeeper Davies' one-day best effort came off 104 balls and contained 14 fours and three sixes.
Earlier, Hampshire were all out for 228 in exactly 40 overs with Sean Ervine's 63 the top score.
Ervine struck six fours and a six in his 70-ball contribution before being one of left-arm spinner Zafar Ansari's victims in his one-day best figures of 4-46.
Hampshire had won their first two matches in Group B, while Surrey - who triumphed in this competition in 2011 - were making their seasonal debut in limited-overs cricket.