In an open contest, both sides created a number of goal-scoring opportunities, but it was Germano's early strike the gave the host a vital three points.
The victory means City extends its advantage in the race for a finals place over Roar to eight points.
Brisbane already fragile defence suffered another blow before kick-off with Jerome Polenz injured in the warm-up and replaced at centre-back by an unfit Jade North.
Melbourne City was missing Aaron Mooy on international duty, but it still began brightly and took the lead inside five minutes.
A Robert Koren cross from deep was played into the penalty spot and Socceroos striker Josh Kennedy rose above his marker to head towards goal. While Jamie Young managed to parry the effort with great reactions, Jonathan Germano was quickest to react and tapped the ball into an empty to give City a 1-0 advantage.
Roar's first genuine attempt on goal came on 39 minutes when Brandon Borello was played into the box by Devante Clut.
The 19 year-old did well to hit the target from a tight angle, but Tando Velaphi was equal to the effort and palmed behind for a corner.
Despite impressing through the contest, City coach John van 't Schip replaced Kennedy with Massimo Murdocca 10 minutes into the second half.
While both sides had chances in the final half hour, neither was able to trouble the goalkeepers to any great extent.
The 1-0 win moved sixth-placed City eight points clear of Roar in seventh, although Brisbane does have a match in hand.
Van 't Schip conceded the significance of the occasion might have affected his players - particularly in the second half - but was delighted at how they were able to absorb the late pressure and go on to record a third straight win.
"Tonight, it was clearly about getting the three points and the tension maybe got in there after taking a very early lead," van 't Schip said.
"In the end, they had a lot of ball possession, but didn't really create big opportunities. I think if we had been a little more sharp on the break, we could've made a second goal and finished the game off.
"But we just have to be happy with the result."
Brisbane boss Frans Thijssen was left to rue his side's inability to convert time in possession into a precious equaliser.
"I think we deserved more," Thijssen said.
"Even in the first half, I thought we were the better team and, in the second half, we were really on top.
"If we get a point here, then you look more positive (for the finals), but now there's not so many games to go.
"It's still possible and we'll still go for it."
