Rilee Rossouw scored his first half-century for Hampshire as Sussex were beaten by one wicket at Hove.
The left-hander was run out for 79 (100 balls) before Lewis McManus clinched the win with a six over mid-wicket.
McManus finished unbeaten on 43 (48 balls) Hampshire won with 12 balls to spare.
Earlier, Kolpak signing Rossouw took a stunning one-handed catch in the slips off Brad Wheal as Sussex were restricted to 230-9 from their 50 overs.
There were two wickets apiece for Wheal, Ryan Stevenson, winter signing Asher Hart on his 20th birthday and Australian Ian Holland, who played for Hampshire’s 2nd XI in 2015.
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