Tasmania 203 (Prestwidge 71, McDermott 42, Scott 3-50) beat New South Wales 158 (MacMillan 3-29) by 57 runs (DLS method)
Tasmania handed NSW their first loss of the domestic limited-overs competition season, triumphing by 57 runs under the DLS method at Sydney's Cricket Central on Tuesday.
Prestwidge - not known for his exploits with the bat - was thrown to the top of the order and blasted 71 off 56 balls with six fours and five sixes, either side of two rain delays that lasted almost three hours.
"I don't know if it suits me," the 24-year-old laughed when asked about his unfamiliar role as opener. "It was great to take the opportunity to get the team off to a really nice start. It would have been nice to go on with it but that's OK ... it was good fun."
Returning to the field at 53 without loss, Tasmania swung freely with 21 overs left to bat and finished all out for 203.
NSW never looked likely to chase down Tasmania's revised total of 216 to win off 30 overs, and were ultimately dismissed for 158 off 26.
Ollie Davies, fresh off his double-century in NSW's Sheffield Shield draw with the Tigers, lost his wicket for 13 at the end of the second over and fellow opener Kurtis Patterson fell two balls later.
Wickets tumbled consistently throughout NSW's chase as the middle order of Riley Kingsell, Ryan Hicks and Will Salzmann couldn't convert starts.
Tasmania's Caleb Jewell ran out Liam Hatcher to end the match after the tailender called NSW top-scorer Jake Scott through for an ill-advised single. Highly-rated offspinner Raf MacMillan was the pick of Tasmania's bowlers.
Prestwidge, who took 1-18 off three overs, said the rain delays made for a "tricky" match. "That's massive for us, going two [wins] from three [matches]," he added.