Sussex amassed their highest total in four friendly matches so far by posting 268 against Gloucestershire at Hove but they still went down to defeat by three wickets.
Tim Ambrose, Robin Martin-Jenkins and Matt Prior all compiled half centuries for Sussex to help them towards a challenging target at the blustery County Ground.
But Gloucestershire's bold reply took them home with seven balls of their 50 overs remaining.
New Zealand Test batsman Craig Spearman set up the visitors by thumping 85 off only 88 balls with a dozen fours and a six.
Spearman shared in an opening stand of 64 with Tim Hancock before former Worcestershire batsman Philip Weston (43) joined him to add 85.
Gloucestershire needed 78 off the last ten overs with six wickets in hand and Sussex's victory hopes were raised when Chris Taylor (42), skipper Mark Alleyne (16) and Mark Hardinges (1) were sent back in successive overs.
But former England wicketkeeper Jack Russell and Jonathan Lewis coolly took their side home as James Kirtley raced in to bowl the penultimate over with 17 needed.
Kirtley sent down a wide and a no-ball, both of which went to the boundary, as the necessary runs came from five deliveries.
Earlier, opener Ambrose laid the foundation of Sussex's useful total by stroking nine fours and three sixes in his 74 off 92 balls.
After Richard Montgomerie and Bas Zuiderent had both fallen for ducks and skipper Chris Adams for two, Ambrose put on 80 for the fourth wicket with Michael Yardy (34).
Prior later joined Martin-Jenkins to share a sixth-wicket stand of a 137, and Martin-Jenkins had cracked seven fours and two sixes off 73 balls in reaching 68 when he was caught at extra cover off Alleyne.
Prior finished unbeaten on the same score having faced only 54 balls and hit seven fours and three sixes.
Fast bowler Lewis followed up his 5-23 the previous day by taking 3-18 in eight overs and Goucestershire's only other wicket taker was medium-pacer Alleyne who had 2-22 off five over.
Scores: Sussex 268-6 (50 overs), Gloucestershire 269-7 (48.5 overs).
Sussex play their next friendly when they meet Worcestershire in a two-day match starting at Hove tomorrow.
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