Then the first of the faithful selections provided a return as import Greg Smith held the top order together with 64 from 115 balls, patiently waiting to strike 10 boundaries.
He was joined by recalled Hamish Harding, who also picked up where he left off at Coastal Cup with 77, sharing a 94-run partnership with Smith before the Englishman was caught out trying to pull.
That triggered another mini collapse, although Wanganui were unlucky to lose two of their veterans as Nick Harding departed for LBW after a long look from the umpire, and then Don Rayner somehow pulled an Andrews delivery from well wide of the stumps all the way back into his castle for 171-7.
Yet Sharrock, who flicked two early deliveries off his pads for well-timed boundaries was about to perform above all expectations.
Even when Hamish Harding finally went at 238-8 after a great knock, Sharrock continued on with Ross Kinnerley (34) and had raced to 76 by the tea break.
The most striking aspect of the innings for witnesses, especially given Wanganui's long list of batting woes, was just how cunning in its simplicity Sharrock's form was.
The young man blocked or left alone any good deliveries and summarily dispatched the bad ones - just like the MCC coaching manual says you should.
After the break, Sharrock's timing temporarily deserted him as he flittered at deliveries, and then the prospect of securing the ton seemed to disappear when Andrews trapped Kinnerley LBW.
Having made a golden duck last time out, No11 Sam Beard heeded Sharrock's pleas to just get in behind the ball, and in fact the tailender played and missed less than his wicketkeeper did, giving Sharrock enough time to push the ball around before finally smashing a tension-relieving boundary to raise his century and let the team declare with 19 overs remaining in the day.
"That one was for my late grand dad," said Sharrock, referencing cycling stalwart Gordon Sharrock, who had passed away the same week Wanganui played Taranaki.
"When I hit my second and third balls through cover for four, I thought there could be something in it.
"It was good to see it through.
"[Nerves] were alright, but as soon as straight after tea with the new ball I couldn't hit a thing.
"I had to dig in and look for one's and two's."
An inspired Kinnerley and fresh Ryan Slight took full advantage of Horowhenua-Kapiti's long day in the field, with over 90 overs being a first for their younger players, as Wanganui tore the heart out of the top order to have them reeling at 42-5 at the close of play.
In-form opener Matthew Good lost his stumps to Slight, while Jarrod Bowick and Jayden Rose were gone with the score at 12. Rayner was accurate at the stumps by trapping Matt Fowler in front and setting up a catch to Sharrock off the just arrived Adam Simonson.
The wind dying down meant rain settled in overnight, leading to a delayed 12.40pm start, and Wanganui managed to polish off the visitors in just over two hours, Horowhenua Kapiti being helped by a fighting 55 from Jamie Pinfold.
Dion Sanson (29), Saturday's sole survivor, tried to bat on before Nick Harding had him off a Sam Beard catch, then Jamie Pinfold was joined by brother Liam (22 not out) to put on 56 for the final wicket.
Kinnerley wasn't having it and dropped several balls short to the brothers, which finally paid off as Jamie Pinfold, having just struck a solid straight drive, had to duck down to the next delivery, before swinging wildly at the last and only spooning the ball high to Slight on the boundary.
At 2.45pm it was a quick trip to the pavilion for some orange juice and biscuits before Wanganui invited Horowhenua-Kapiti to have another go - needing 198 to make them bat again or trying to get through to the 7.30pm finish.
Gillespie was asked what had brought about such a turnaround in 13 days.
"Ownership. They've made their own decisions and don't want a repeat of the last game.
"We bowled and kept the pressure on, bowling in pairs, for all of it except that last half an hour.
"It's quite pleasing."
Still, Gillespie remembered from the Taranaki match just how quickly events can turn around, and while first innings points had been comfortably secured, it was going to take a big ask to get the visitors out twice on a deck which was flattening out, with rain also a looming prospect.