Jake Stringer, the substitute on return from a hamstring injury, kicked the match-winning goal at Engie Stadium to set up the 16.10 (106) to 14.15 (99) win on Sunday.
The Suns had looked set to cruise to an easy victory after slamming through the opening four goals, but the Giants stayed true to their 'never surrender' attitude.
With 22 points the deficit at the final change, Adam Kingsley's men opened the fourth quarter with four straight majors.
It was 50-gamer Aaron Cadman's third of the afternoon that launched the Giants ahead for the first time, earning a two-point margin.
But a maturing Suns outfit remained determined, and Brayden Fiorini responded to restore the visitors' lead.
Substitute Stringer, in his first game since round nine, then proved his quality to restore the advantage for the Giants with a dribbling ball from the right pocket.
He later helped seal the deal with another from the opposite pocket in the 28th minute of the quarter.Â
The Giants hold onto their top-eight spot (9-6) with their fifth-straight win over the Suns, their 15th overall since the two expansion clubs' inaugural 2012 season.
Sunday's meeting was the first time both the league's youngest teams were in the top eight.
Gold Coast, who have yet to make a finals series, have dropped out to ninth (8-5) through three consecutive losses, but have played at least one game less than all the teams above them.
"In theory, they're (Gold Coast) sitting third or fourth on the ladder in games in lieu," Kingsley said.
"To come away with a victory that maybe didn't look likely halfway through the first quarter, particularly, was quite emotional."
Suns coach Damien Hardwick, Kingsley's former mentor, was left "just flat".
"We did a lot right throughout the night," Hardwick said.
"Unfortunately, when push comes to shove in big games like today, you've got to nail those moments and we just didn't."
Suns captain Noah Anderson orchestrated their early dominance, and finished with a game-high 15 score involvements from 42 disposals and seven clearances.
He was well supported by Touk Miller (37 disposals, seven clearances, two goals) and Matt Rowell (34, four).
Tom Green led the way for the Giants with 30 disposals and 16 clearances, while Lachie Ash had 33 touches.
Ash was without his defensive partner Lachie Whitfield, who suffered a concussion in the first quarter.
Attempting to salvage a mismeasured kick by teammate Toby Bedford, Whitfield was involved in a side-on collision with Suns forward Ben King.
Whitfield was replaced by Stringer in the second quarter.
GWS were already without Whitfield's fellow All-Australian backman Sam Taylor (foot).
The Suns took advantage of Taylor and Whitfield's absence, slamming through four-straight goals in 16 minutes before the Giants managed their first score - two Jake Riccardi goals - in the opening quarter.
Jesse Hogan reduced the deficit for the Giants after Suns defender Mac Andrew mistook a 'play on call' by a teammate and moved off his mark, giving away a 50-metre penalty.
Gold Coast took 23 inside-50 entries to 10 to finish with their highest-scoring first quarter of the season, leading 7.6 (48) to 4.1 (25).
The Giants lifted in the second term but could only kick two goals to one to reduce the deficit to 13 points.
GWS finally came alive when Cadman slotted his second of the afternoon to open the final quarter.
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