Eight points clear of seventh-placed Adelaide with three games remaining in the regular season, Sunday's win made it nine games without defeat for Alen Stajic's side as they surge towards what would be just a second A-Leage Men finals appearance in eight seasons.
The Wanderers now sit fourth, just two points behind third-placed United and four off second-placed Melbourne City, who will make the trip to Wanderland next Saturday.
"I thought (tonight) would be a real finals-type game," Stajcic told Paramount+.
"It was always going to be moments of quality to decide it; it was just two excellent teams going at it."
Despite having the best of play in the opening 45 minutes at CommBank Stadium, the Wanderers looked set to be held goalless at the break, especially when Gersbach put too much weight on a pass for Brandon Borrello on the stroke of halftime.
But the Socceroo attacker didn't give up on the ball and sprinted to keep it in play before turning inside to find Gersbach's continued run, setting the defender up to dink his first ALM goal, over United keeper Matt Sutton.
He was unlucky not to be awarded another in the 66th minute when he attached such wicked inswing to a corner that Sutton could do little more than palm it into his net.
"It's starting to click at the moment, so we're just going with it," Gersbach said.
The two-goal cushion arrived at a crucial moment for the hosts, who were outshot by nine shots to four in the second half and had just survived two lethal-looking attempts from Hiroshi Ibusuki through a combination of super goalkeeping from Lawrence Thomas and some desperate scrambling defence.
"The second half, we were very good," United boss John Aloisi said.
"We've scored so many goals of late and tonight was one of those nights that the ball didn't want to go on the back of the net."
A five-game winning run featuring 19 goals now snapped, United slipped to third and missed out on the chance to draw within three points of leaders Auckland, who will travel to Ironbark Fields on the final day of the season.
