The Melbourne brothers were in opposition in this rousing battle at Dooradoyle at the end of which visitors Young Munster emerged as four-point winners.
The younger of the two brothers, Munsters' number 8 Neville Melbourne, had reason to celebrate as his side staved off some persistent late pressure from the Light Blues to take home a valuable four points.
Winning back-to-back local derbies – they beat Shannon last weekend – gives Young Munster the Limerick bragging rights going into a three-week break in Ulster Bank League action.
A try by their player-coach Mike Prendergast, ten minutes from the end, made all the difference and while both sides squandered scoring chances, Young Munster just about deserved the victory.
A player from each side, Young Munster prop Alan Cotter and Garryowen's strong-running number 8 Lemeki Vaipulu, were sin-binned on separate occasions in a first half which was tied at 3-3.
Willie Staunton kicked a penalty and then crucially converted Prendergast's try which came following sustained pressure on the Garryowen line.
Young Munster had an early chance when Garryowen were penalised for collapsing a scrum but Staunton's penalty attempt from the right near the touchline drifted wide.
Cotter was flashed a yellow card after 28 minutes and goal-kicking centre Alan Gaughan managed to send Garryowen in front with a crisply-struck penalty.
The lead lasted only four minutes however, as Garryowen were penalised in rapid succession and when one of their players gave backchat, they gained an extra advantage from which Staunton landed the penalty.
It was a scrappy first 40 minutes and the tension was obvious with both Staunton and Gaughan missing kickable penalties and a number of passes being dropped.
There was more in the way of attacking play in the second period, a hack through from Munsters centre Andrew Burke and a follow-up almost got him over for a try. But Gaughan got back well for Garryowen.
Just on the hour mark, scrum half Fergal Lawlor fired over a penalty from in front of the posts to make it 6-3 to the Light Blues.
But then came Prendergast's try. Munsters turned down a kick at the posts on three separate occasions, opting to set up a series of lineout mauls.
Garryowen managed to hold out until from a five-metre scrum for the visitors, the ball squirted loose and an alert Prendergast pounced to score.
Staunton added the extras to clinch a famous Limerick double for the Cookies, who defended stoutly late on in the face of mounting pressure from Garryowen.
Referee: Olly Hodges (IRFU)