Trailing by two points at the final break, the Giants slammed through five goals to two to set up a 16.7 (103) to 13.11 (89) victory at ENGIE Stadium on Saturday.
It is a heartbreaking result for an unfancied Bombers side (1-8), who had led by a game-high 26 points in the third quarter.
GWS, rising to 13th, nabbed their fourth win after losing four more players to injury earlier in the week, star goalscorer Jesse Hogan (hip) among them.
Ever-reliable defender Connor Idun personified the club's 'never say die' attitude with a desperate smother to deny a certain goal from Bombers youngster Jayden Nguyen.
"I'm not sure our grit has ever been questioned," Kingsley said.
"That epitomises what many of our players do in big moments.
"Now we'd certainly like to be not in those moments where we need a massive smother to save a goal, but the opportunity's there.
"It was Connor's turn this week. It'll be Jack Buckley next week, or it'll be Jayden Laverde."
Ex-Essendon spearhead Jake Stringer kicked three goals and Hogan's replacement Max Gruzewski slotted two, while Giants recruit Laverde (11 intercept possessions) impressed as the last line of defence in his first match against his former side.
Essendon remain second last after falling short of their second win of the season, with a shoulder injury to impressive first-year player Dyson Sharp only adding to their woes.
Still, Essendon coach Brad Scott was also left proud of his young side's effort.
Archie May and veteran Peter Wright both kicked their third goals of the game in the final term, while 20-year-old defender Archie Roberts led the game with 42 disposals.
In his 100th match, milestone man Sam Durham took eight clearances.
"We're impatient like all of our fans are, but we want to make sure that we're building a solid foundation," Bombers coach Brad Scott said.
"It was never (going to be) any quick fixes, that we were going to come in and just snap our fingers and get it done.
"As a coach, you don't expect 18-year-olds to be the backbone of your side, but very quickly they are becoming that."
Bombers youngster Xavier Duursma booted two majors in a tight opening quarter, but fluffed his chance for a career-best third as the Giants took a four-point lead to the main break.
Just as he did with the opener, GWS skipper Toby Greene outworked counterpart Andrew McGrath in front of goal to kick off the second quarter.
But Greene's goal would be the home side's only major in the term, with Essendon upping the ante.
Unable to withstand the pressure, GWS trailed 15 points at halftime.
It was the second time this season the Bombers led at the main break, last doing so in their round-six loss to Gold Coast.
A red-hot Fremantle side out to equal a club-record run of nine wins is up next for Scott's side, while GWS travel to play West Coast.
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