The Melbourne Victory-bound striker endured a nervy game at Suncorp Stadium but done enough to lead the Roar to victory.
Berisha was playing in his first game since his move to Melbourne Victory next season was made public, and despite a scrappy 89 minutes by his own standards, he managed to pop up at the death seal a dramatic 2-1 win for his side.
The Roar dominated possession but went into the break trailing 1-0 thanks to a Mile Sterjovski penalty.
After half time, however, Thomas Broich orchestrated a scintillating attacking performance from the home side, who drew level thanks to Henrique before Berisha's late goal.
Mulvey maintained that his star striker was somewhat nervous throughout the match.
Berisha's first touch let him down on a number of occasions and he took an air swing at a close range chance in the 35th minute which he would normally put away with little fuss.
"The best strikers in the world, they're quiet for 89 minutes and then they score a goal," Mulvey said after the game.
"And if that's what it takes, then I'll take it every week.
"It's actually interesting because he probably passed up a couple of chances that normally he would finish so I think there might have been a little bit of nerves there for him today.
"But delighted for him because he's had a very tough last couple of weeks.
"He's had to make a very difficult decision based on economics and Australian football.
"I knew during the week that he was in a happier place because he was training very well, and he won us the game today."
The Roar manager said Berisha's nervousness was based on a willingness to give his all for the home fans, who supported him well throughout the match despite his pending departure.
"He wants you to give you everything," Mulvey said.
"And I think I know today that he wanted to give Brisbane everything.
"Not just me, the players, his teammates, his family, he wanted to give them everything.
"And that goal means the world to him because he feeds off that, that's his personality."