Second seed Fitzgibbons, 21, produced a score of 16.00 in the heats before securing a quarter-final victory over France’s Pauline Ado.
That high score was only bettered by 24-year-old Gilmore’s 16.26, also set in the heats before she was sent packing by Hawaiian Ho later in the day.
“Everyone was struggling to get waves and there were only a few opportunities to get scores,” Fitzgibbons said.
“It’s really nice to have a good start to the heat. I was just hoping to find a couple of those rights and hopefully the swell picks up for the remainder of the event.”
Ho , 21, put in a superb performance in besting four-times world champion and current rankings leader Gilmore on two occasions.
Ho won her three-woman round three heat and went on to dominate Gilmore in the quarter-finals by a score of 14.93 to 7.23.
“It was definitely crunch time in that man-on-man heat and Steph is trying to win a world title and I’m trying to re-qualify and get a really good result,” Ho said.
“There definitely weren’t as many jokes and laughs as the last heat.
“Steph had priority most of the heat and kept taking the first one and somehow there started being more waves in a set and I kept getting really lucky.
“I’ve had a pretty bad beginning to the year and anything from here on out is a bonus. I’m looking forward to finishing up the year strong.”
Despite an otherwise-solid run in the event, Gilmore admitted the defeat has dealt a big blow to her hopes of claiming the 2012 world title.
“It’s always tough to lose in conditions like this,” Gilmore said.
“That’s competition though and we all have to deal with the same field of play. The window for our event here was never going to have the best waves and would likely favour some of the surfers that excel in these conditions.
"Brush it off though and focus on the next one. There are still two more events and that will have a major bearing on this year’s title race.”
BILLABONG RIO PRO WOMEN’S QUARTER-FINAL RESULTS:
QF 1: Alessa Quizon (HAW) 12.77 def. Courtney Conlogue (USA) 12.50
QF 2: Coco Ho (HAW) 14.93 def. Stephanie Gilmore (AUS) 7.23
QF 3: Sally Fitzgibbons (AUS) 10.50 def. Pauline Ado (FRA) 9.17
QF 4: Carissa Moore (HAW) 8.32 def. Laura Enever (AUS) 8.33
BILLABONG RIO PRO WOMEN’S ROUND 4 RESULTS:
Heat 1: Alessa Quizon (HAW) 12.56 def. Lakey Peterson (USA) 10.87
Heat 2: Stephanie Gilmore (AUS) 16.26 def. Tyler Wright (AUS)11.44
Heat 3: Pauline Ado (FRA) 12.10, def. Rebecca Woods (AUS) 10.33
Heat 4: Laura Enever (AUS) 13.10 def. Malia Manuel (HAW) 9.60
BILLABONG RIO PRO WOMEN’S ROUND 3 RESULTS:
Heat 1: Courtney Conlogue (USA)11.87, Alessa Quizon (HAW) 11.66, Tyler Wright (AUS) 7.96
Heat 2: Coco Ho (HAW) 15.40, Stephanie Gilmore (AUS) 15.07, Lakey Peterson (USA) 13.30
Heat 3: Sally Fitzgibbons (AUS) 16.00, Rebecca Woods (AUS) 12.16, Malia Manuel (HAW) 10.50
Heat 4: Carissa Moore (HAW) 11.83, Laura Enever (AUS) 11.67, Pauline Ado (FRA) 10.20