Wanganui's Henry Kilmister (3-28 from six overs) and Adam Lennox (2-22 from seven) were the pick of the bowlers.
However, the Aucklanders quickly adjusted and Wanganui lost a thriller by just one run, being dismissed in the 29th over for 121, with Sam Sherriff the main contributor with the bat, scoring in the 30's.
Coach Jason Clark said the leading lights in the Wanganui team were now getting very tired, some of them having played for six days straight in the other Wanganui age group teams during the festival.
Wanganui rebounded to beat Manawatu yesterday morning by eight wickets.
They dismissed the team in green for 106, with the best batsmen being Wanganui's own Ben Strang, who was filling in for the understrength visitors and scored 37 not out.
Geordie Ellis (3-9, four overs) and Joel Clark (2-20, seven) were the pick of the bowlers.
Wanganui reached 107-2 in 21 overs, with Henry Deans (35 retired) and Harry Godfrey (27 not out) the pick of the batsmen.
At press time yesterday afternoon, Wanganui was playing South Taranaki in the first T20 game, while Parnell took on Manawatu. The two winning teams meet in the final this afternoon. The final round robin games of the 35-over format are played this morning, with the final being played tomorrow.