England winger Tom Johnstone was left in agony and needing oxygen on the pitch after an innocuous tackle by Ratu Naulago in the 35th minute.
After a lengthy stoppage, he was eventually stretchered off but thankfully was able to resume his place on the sideline in the second period, admittedly with the aid of crutches and his left knee in a brace.
Dream Team centre Bill Tupou scored two tries but also left the KCOM Stadium on crutches after being helped off late on as Trinity defied the odds to secure victory.
They had been 14-0 up when Johnstone - who suffered a ruptured ACL in 2017 - was injured yet saw 12-man Hull fight back to 14-12 by half-time.
When Kirmond was then sin-binned for a late challenge as Marc Sneyd kicked ahead in the 48th minute, they could easily have feared another game slipping away just as it did against Hull KR on Sunday.
However, just like Hull, Chris Chester’s side also blossomed when at a numerical disadvantage and eventually powered home for what the head coach described as the "best win" of his time at Belle Vue.
After the hosts had spilled following Kirmond’s indiscretion, they scored with their next attack, Tupou, who switched to wing in Johnstone’s absence, scoring his second try from Ryan Hampshire’s fine pass.
Danny Brough added a penalty on the hour mark and Hull’s hopes of a fourth successive win were ultimately ended with some mindless play by Sneyd three minutes later.
The two-time Lance Todd Trophy winner dabbed a kick through but, having failed to reach it before rolling dead, then hacked the ball into the stand.
Referee Liam Moore had no option but to give the scrum-half a yellow card; his side were just 20-12 down at that point but any chance of a victory disappeared with him.
Pauli Pauli powered over for another try and Brough also added a penalty before Sneyd returned.
Reece Lyne completed the victory but a fourth player was sin-binned when Pauli was marched for a high tackle on Joe Westerman in the final seconds.
David Fifita was outstanding for the visitors, especially in his first spell when the prop skittled Hull defenders with regularity while Hull’s brightest player was Jez Litten, the young hooker who sparked them off the bench.
There had been no score from either side until Ryan Hampshire scored a spectacular length-of-the-field try in the 27th minute.
Wakefield looked to have caused chaos near their own line as a ball out of dummy-half rolled past their own posts.
But, as is so often the case, a bouncing pass turned out to be the best pass; Johnstone cleaned things up and bumped off some defenders in the middle before finding Lyne who sped clear.
The England Knights centre, in turn, found Hampshire motoring up in support and he had a clear race to the line from halfway.
Brough converted and, just four minutes later, he added a penalty after Albert Kelly was sin-binned.
Tinirau Arona had slipped prop Craig Kopczak through from halfway and just as Kyle Wood arrived to carry things on, the Hull stand-off unceremoniously clobbered the diminutive hooker.
It was hard to gage initially if there was anything illegal about the challenge but, after consulting his touch judges, Moore deemed it worthy of a yellow card.
Wakefield quickly made the extra man count, Brough’s fine long ball expertly helped on by Matty Ashurst for Tupou to scurry over.
Brough improved and his side had scored 14 points inside just five minutes.
Then came Johnstone’s injury and Hull’s brief comeback with two quickfire tries that left them narrowly behind at the break.
After Sneyd’s grubber, captain Danny Houghton picked the pockets of Wakefield counterpart Jacob Miller behind his own posts to score.
Sneyd converted and soon after dabbed in another kick to the corner which this time saw an alert Bureta Faraimo win the race ahead of Ben Jones-Bishop.
Sneyd improved from wide out with the final kick of the half but his moment of madness was his lasting mark.
Hull FC: Shaul; Naulago, Tuimavave, Griffin, Faraimo; Kelly, Sneyd; Taylor, Houghton, Matongo, Minichiello, Manu, Westerman. Substitutes: Hadley, Thompson, Litten, Ellis.
Wakefield Trinity: Hampshire; Jones-Bishop, Lyne, Tupou, Johnstone; Miller, Brough; Fifita, Wood, England, Kirmond, Ashurst, Crowther. Substitutes: Horo, Kopczak, Arona Pauli.
Referee: Liam Moore (Leeds)