Although the scoreline wasn't a million miles away from the classic, 83-pointer these expansively-minded sides put together last season, this AIB All-Ireland League performance was, in its own way, a much more impressive display of St Mary's title aspirations. They're starting to look the part.

As expected, a young, cocky, irreverent Blackrock put it up to St Mary's in what little rugby Murray Whyte permitted during a staccato first-half. But, with some similarity to last week's Lansdowne Road international, St Mary's went ahead through a key, pre-interval try and then turned the screw in the third quarter.

The victory was garnished by tries from their trio of international wide runners, Kevin Nowlan, John McWeeney and Dennis Hickie, as well as one from their young, international centre in the making, Gareth Gannon, as St Mary's exposed Blackrock defensively out wide.

But this was a classic case of "forwards win matches, and backs by how much".

The official man-of-the-match award went to Eoin McCormack, who deputised impressively for the absent Conor McGuinness. McCormack's sniping breaks were a constant thorn in Blackrock's side.

These things are, admittedly, purely subjective, but the player who did more than most to lay the victory platform was undoubtedly Victor Costello. The big man is putting together the most impressively consistent form of his career and is proof that some players can flourish more in the domestic game than across the channel.

Costello consistently made huge yardage, picking up and going from the base of the scrum or rucks, breaking through the gain line and sometimes requiring four or five Blackrock men to bring him down like sketches from a comic book. At times he seemed unstoppable.

This also served to suck in the defence and leave Blackrock a little punch drunk, so that by the end the likes of Emmet Byrne and Steve Jameson were also punching big holes in a waning defence.

Furthermore, Costello frequently drew opponents to create gaps for the likes of McCormack, a significant factor in the crucial Nowlan try when Costello fed McCormack and the full-back gathered the scrum-half's looped pass high and left-handed to elude Brian Scally's tackle and round the posts.

This performance was also compelling evidence that Costello will wreak even more havoc with Trevor Brennan alongside him. Brennan, harshly cast adrift from Wednesday night's A squad to play the Canadians after one poor performance in the Development Exiles trial, when he unwisely played with a back injury, made a big impression without any of the trademark big hits.

A hard-running foil to Costello, Brennan too consistently took the ball over the gain line, either offloading in the tackle (an area of his game that has come on a ton) or giving his rucking forwards a target on the ground from which many points were accrued.

It was during the third quarter, particularly, that Costello and Brennan sewed the seeds of victory. And one short restart by Alan McGowan meant that Blackrock, in effect, didn't have the ball for 17 minutes, during which time St Mary's pulled clear.

A contented Hugh Maguire, cocoach along with Steve Hennessy, said: "We are happy with that. In the third quarter, we turned the screw and began sucking in the defence to create the gaps out wide, rather than fire the ball out just for the sake of it. That's a starting point, but we've got to start playing for 80 minutes.

"For me, Victor had an outstanding game and was closely followed by Brennan. When they got up a head of steam, Rock struggled to cope with them."

It was a potent mix, varnished by the accurate throwing of Barry Browne, and the all-round effectiveness of Steve Jameson, who is yet to miss a competitive club game in his entire career, and still poaches opposition ball, wins his own and makes try-saving tackles in the corner late on.

St Mary's also have unequalled strength in depth at half-back, and then there are those three strike runners.

Hickie, the most potent runner in the league, only needs two yards and he's gone; the classylooking Nowlan is oozing confidence, and, encouragingly, McWeeney has retained his confidence despite being cast adrift for a converted centre by Ireland after a nerve-wracking debut against the All Blacks.

Blackrock have three backs to return from injury - Michael Jackson, David Quinlan and Brian Carey - but they're short a tight-head, and have none of St Mary's big runners up front. Realistically, with up to four teams tottering beside the relegation trap door, this is another season about survival.

Tony Smeeth, the Blackrock coach, maintained that Nowlan's score "was a soft try. We lost faith in our defence and you can't give Nowlan space like that. We defend from the outside in and Aidan Guinan stayed out on his man (Hickie) as Scally was drawn in by McCormack. I thought we had been the better team in the first half, and certainly played more of the rugby."

That said, he conceded that Costello and Brennan had been the difference thereafter. "To be honest, I didn't think St Mary's could win the league until I saw them today. But after today, now I think they can. They can do what Shannon can do, namely, they can keep the ball."