Dropped from the squad that lost to the Brumbies last week, Wallabies hopeful and code-hopper Vunivalu was heavily involved in a 40-28 win at Apia Park on Friday.
The victory was the Reds' first abroad since a 2019 win in Durban and ended a three-game Super Rugby Pacific losing streak.
Approached with caution given it was Moana's first game in Samoa, the comfortable win took some pressure off coach Brad Thorn and boosted the Reds' finals hopes as they improved to a 3-5 record.
But they left a bonus point behind, two late Pasifika tries denying the visitors the extras that could prove crucial in the season wash-up.
Vunivalu's stocks rose with the winger scoring from an intercept after having a hand in two other first-half tries.
He linked up well with carving halfback Tate McDermott, who, along with Vunivalu, was not included in Eddie Jones' first Wallabies training camp that will gather next week.
McDermott found gaps in the host's defence early and it was Vunivalu in support, the winger offloading to Fraser McReight for the first try and then making another break that led to the first of hooker Matt Faessler's double.
When Vunivalu plucked a pass from mid-air and stepped back infield for a solo try it was 28-14, the Reds' set piece dominant in the second half to ensure no fairytale comeback by the hosts.
Faessler went over behind a rolling maul before James O'Connor, playing inside centre, beat four men and offloaded for No.10 Lawson Creighton for the Reds' sixth and final try in the 54th minute.
Thorn, off-contract beyond this season, could afford a smile after a win to snap a rough month.
"We needed that," he said.
"There were some good moments, there were some errors.
"And that (losing the bonus point) was frustrating ... with a lot of teams around us (on the ladder), those things add up and are important."
The home crowd still had plenty to cheer, Miracle Faiilagi scoring twice at the ground just down the road from his childhood village.
His first finished a terrific full-field effort while centre Danny Toala made it 14-14 with his try.
Forward passes robbed the hosts of two more tries, the Reds doing as they pleased either side of those to ensure Moana remained winless this season.
"You can feel the disappointment there," proud coach Aaron Mauger said.
"We played some outstanding rugby tonight; just those little moments cost us but we'll keep working hard."