"Just gutless. The whole thing was really disappointing. I've got no words for it," said Gillespie.
"Very, very frustrating."
Dominic Lock, Morgan Inness, Mathew Boswell and Greg Smith all had failures in one or both turns at bat, while John McIlraith came back from a duck to top score with 46 in the second innings when entering at No6 after the swap with Harding.
The lower order of Hamish Harding, Dominic Rayner and Chris Sharrock have all had their moments with the bat this summer, but added nothing at the oval.
"There were three dismissals where they were genuinely gotten out by the opposition," said Gillespie. "The other 17, it was poor shot selection and being in a hurry. You'd think it was Twenty20 cricket."
There were six wicketkeeper catches in the first innings and being caught out in the field marred the second dig, with Gillespie saying too many players just threw the bat at deliveries they should have let go.
"They couldn't bat time. The bowlers put it in the spot and we helped them."
Daniel Ingham finished with 5-13 from his nine overs to take a seven wicket haul in the match, while Dean van Venter picked up two more scalps to go with his four-for in Wanganui's first innings.
Wanganui had been in a good position when they had the hosts at 144/6 on Saturday, but with a wet ball in the final session they let Paul Lyttle (76) and captain Gordon Reisima (94) get away from them and post a 300-plus total which proved too intimidating.
Regarding who the team can bring in over the next fortnight before the scary prospect of facing Hawke's Bay on February 13, Gillespie was glum as the options are few.
Teenager Connor O'Leary was to debut at the weekend but had stitches in his hand which became infected, leaving him in a sling on Friday while Josh Trillo was called in at short notice.
Both O'Leary and a returned Ryan Slight would strengthen the bowling unit but Gillespie admits they could not have done much to have changed the weekend's outcome.
Ben Smith will be entering into the Ford Trophy campaign for Central Districts, so the only other prospect would be a plea to Tom Lance to play just one weekend of representative cricket, after returning a fortnight ago for Property Brokers United following his long absence with a groin injury.
"That's a conversation I'll be having with Tommy to see where he's at," Gillespie said.
But with Mark Fraser out injured this summer, the coach said everyone else who could succeed with the willow is already in the team.
Adding to Wanganui's sense of disappointment should be the events down south where the Hawke Cup has changed hands after tiny Buller, getting their first challenge in 106 years, defeated Canterbury Country on first innings points in Rangiora at the weekend.
Buller chooses their squad from just four adult teams in Westport - a pool of 25 players - and play all their club cricket on artificial wickets.
Yet that did not stop them bowling well and batting time under pressure to cause a famous upset, and offer a timely example if Wanganui are paying attention about how to play above yourself on the big stage.
Scoreboard
Wairarapa 1st Innings
323/8 dec (63 overs).
Wanganui 1st Innings
121 (44.5 overs).
Wanganui 2nd Innings
N Harding ct M Hughes b D Ingham 30
M Boswell b D Ingham 3
D Lock lbw b D Ingham 7
M Inness ct M Hughes b D van Deventer 22
G Smith ct G Deans b D Ingham 0
J McIlraith ct D Ingham b S Hook-Sporry 46
H Harding ct R Speers b D van Deventer 13
D Rayner ct R Speers b K Fahey 4
C Sharrock ct P Lyttle b D Ingham 1
J Trillo ct P Lyttle b S Hook-Sporry 6
R Kinnerley not out 3
Extras: 11
Total: 146 (41.1 overs).
Bowling: D van Deventer 8 overs, 0 maidens, 35 runs, 2 wickets; S Hook-Sporry 12.1-2-36-2; D Ingham 9-2-13-5; B Price 5-2-12-0; G Deans 6-0-36-0; K Fahey 1-0-5-1.
Result: Wairarapa won by an innings and 56 runs.