Newcastle were handed the premiership earlier on Sunday when Auckland FC lost 1-0 to Central Coast Mariners at home.
The result also gifted Adelaide the opportunity to close the gap on second-placed Auckland to just one point if they could defeat the Bulls at home.
United were dealt a blow early when Mitch Duke found the back of the net to help Macarthur to a 1-0 halftime lead. Andrioli introduced Anselmo and Brody Burkitt at the interval and the impact was almost immediate.
Anslemo scored on 63 minutes with a powerful header before Pana Kikianis put the Reds in front. The Brazilian then capped an impressive individual performance with a finish from close range in the 89th minute.
Andrioli applauded the 37-year-old, who has endured an injury-riddled start to life at the Reds.
"First of all I'd like to say I'm extremely happy for him because he went through a tough time," he said.
"He came here, he had expectations to play, help us and then had a few difficult moments with injuries, he couldn't train, couldn't get himself fit. He was down for quite a long period of time but credit to him.
"I always had belief and confidence in what he could do if he was healthy and fit so for that reason I'm really happy for him. I have no doubts the way that he's been coming into the game, he's a player that can have an impact for us."
United sit third following the victory against Macarthur, two points clear of Sydney FC and fifth-placed Melbourne City, who the Reds face on Sunday in Melbourne in the final match of the home and away season.
Sydney and Auckland will meet earlier in the day and the result of that match could determine the Reds' fate. A win for Auckland would rule out a second place finish for the Reds while Andrioli knows only a win will do for his side.
"What an opportunity to play this game against Melbourne City next week," he said.
"I'll say like I've been saying the whole season - the most important match is the next one and this is the most important game and we will go there prepared to play and win the match.
"We will prepare in the best possible way like we have been doing all season and we're going to go to Melbourne with a lot of confidence."
Ninth-ranked Macarthur takes on seventh-placed Wellington Phoenix at home on Friday night, with both sides unable to make the finals.
Coach Mile Sterjovski is hoping to end the campaign on a positive note with victory in front of Macarthur's supporters.
"We still want to finish on a high in front of our home crowd so we will focus on next week and we want to get a result," he said.
