Meredith's fast bowling saw him take 4-16 off eight overs and Blackley used his quick left-armers to have 2-20 from three overs.
The visitors were reeling at 49-9.
However, Manawatu's final pair would likewise not be dislodged, as Wanganui had a couple of near-run outs from direct hits in the field, but also dropped a couple of regulation catches and gave away 35 extras in the innings, allowing the visitors to get home in a thriller.
Matthew Hocquard bowled five maidens and conceded just six runs from his eight overs, while Harry McVerry sent down three maidens and gave up just four runs in his five overs.
Taihape's Abernethy twins – Saul and Geordie – bowled straight and fast but also received no reward.
Team players of the day were Meredith for his bowling and Gardner for his batting.