Trailing by five points at three-quarter time, the Suns hit the lead with five minutes left for the first time since early in the third term thanks to a superb goal on the run from co-captain Niamh McLaughlin
Richmond had two golden opportunities to reclaim the lead through Emelia Yassir and debutant Shelby Knoll, but they both missed.
The Suns were able to score another two quick goals from Darcie Davies and Havana Harris, ensuring they won 5.9 (39) to 3.7 (25).
Gold Coast finish the season 2-10 - the same record as Richmond and GWS, but their percentage means they finish 18th and last.
"Obviously delighted to get the win," McLaughlin told Fox Footy.
"A tough season for both teams.
"Last time we came here against Richmond, two years ago was very similar, so we knew that it was always going to be a very tough game and go right down to the wire like that.
"We worked hard for it, and in the end we probably deserved the win overall.
"Probably relief is the biggest thing.
"Just within the group we've fought very hard.
"I know from the outside, people will say what they want, but we're building in the group, and we have trust in what we're doing, so we're just hoping to build on that for next year."
Charlie Rowbottom (32 disposals), Lucy Single (29) and McLaughlin (23) were outstanding for the Suns.
Yassir was the only multiple goal-kicker on the ground with two, but could have had three and she would be regretting her late miss.
Reigning league best-and-fairest winner Mon Conti had one of her quieter games, gathering 20 possessions and failing to win a clearance.
Richmond are set for a big off-season, with former Carlton football boss Brad Lloyd to review the Tigers' football department after a bitterly disappointing campaign.
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