Oxfordshire went down to Worcestershire by two wickets in a low-scoring encounter at Hagley Hall on Wednesday.
Oxon need to beat Shropshire next week to make sure of qualifying for the knock-out stages.
After choosing to bat first, the visitors slumped to 83-9 before a last-wicket stand of 61 between Neil Megson and Ian Curtis helped them to 144-9, Megson finishing with 50 not out.
That total looked enough when Worcestershire collapsed to 85-7 against Curtis and Darryl Woods.
However, Gary Mills hit an unbeaten 44 to see them home by two wickets with an over to spare.
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