All had been going well to begin with, as Whanganui took a 3-0 lead into halftime, after Tony Gilbertson opened the scoring after a tap in to an open goal following a breakaway, then a returning Lee Moir made a reverse stick shot where the College B keeper had been standing a second before.
James Craig gave them further breathing space with his shot taking a deflection off a defender into the goal.
But from a comfortable perch, Whanganui found themselves deadlocked 3-3 going into the final period.
"Not a lot of chat, I think everyone knew they'd lost their heads a little bit," said Wilbur.
"All three of their goals were really quite soft."
Whanganui had been guilty of running when they shouldn't or letting off bad passes.
Regaining their shape, they pulled the match out with two goals by the talented Travis Bayler inside the last five minutes.
"[College B] had a very strong team on the field," said Wilbur.
"Eight out of the 16 have been involved at some point when we played them [College A] last year in Premier."
Whanganui must now figure out the formula to beat the only team that has defeated them this year, with HSHC A picking up 5-3 and 3-0 wins in July.
They will be without Craig Ritani (wedding anniversary), while Josh McDonnell (hamstring injury) still remains unlikely.
"Otherwise, it should be all hands on deck," said Wilbur.
"But it will need a much improved performance."
The Whanganui Women's season ended in their Premier Women's semifinal against the undefeated College A, who were taking no chances against a plucky underdog side that had managed a draw against them this year, shooting accurately for a 7-0 win.
Fielding a strong lineup that included former Black Stick Kayla Whitelock, NZ Under-18s coach Verity Sharland, and Whanganui's expat Junior Black Emma Rainey, College moved the ball well and most importantly finished off.
Whanganui captain Colleen Baylis said they had their fair share of opportunities from penalty corners and strokes, but could not find a way through.
"I don't know how HSHC A are going to stop them [in the final].
"We went down there with 14 players and ended up with 12.
"But I don't feel it hindered us, because the players we had stepped up."
Lucy Tui gave another committed performance on defence, while goalie Sienna King ensured the scoreboard did not blow out any further.