Tom Haines tuned up for the 50-overs campaign with a century.
The Sussex opener made 102 off 110 deliveries, including ten fours and two sixes, in a 58-run win over Hertfordshire at Arundel.
First-class counties are preparing for the Metro Bank Cup by playing minor counties.
Haines shared an opening stand of 179 in just 26.2 overs with Tom Clark, whose 96 came off 83 balls and featured 13 fours and two sixes.
The momentum was lost until Jack Carson fired 48 not out from just 17 balls at the end of the innings, with four fours and four sixes.
Hertfordshire also had a strong foundation with the first wicket worth 170.
They then fell away and were all out for 282 as Carson took 4-51 and Fynn Hudson-Prentice, Henry Crocombe and Archie Lenham two wickets apiece.
Sussex visit Berkshire in Slough on Tuesday before opening their competitive programme away to Notts on Sunday.
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