If there has been a better day in Kilkenny College's fledgling rugby story nobody at Donnybrook yesterday could recall it. Accordingly yesterday's deserved quarter-final victory over one of the favourites and four-times winners constitutes something of a landmark as well as a major upset.

The reward is a place in the semi-finals, in only their second season in the stronger section, courtesy of an injury-time penalty by their captain, Russell Armstrong. Yet they won in some style, and fittingly the final score reflected their willingness to run the ball and counter-attack from practically anywhere.

St Mary's will know they could have played better and were severely undermined by the absence through injury of their Irish Schools' international Shane Jennings. By the time he was introduced for the last 21 minutes not even he, his left knee heavily strapped, could save them.

Yet even though Armstrong missed a couple of first-half penalties as St Mary's conceded eight penalties to one in that period, and with St Mary's surprisingly struggling to play with their customary tempo, the script initially panned out as planned.

Ten minutes in, a fortuitous bounce gave St Mary's a close-range line-out from which captain Conor Queenan gathered and fellow lock Eoin Higgins claimed the touchdown in the ensuing drive. Their powerhouse right winger Cathal Connolly was looking the most potent back on view, his pack generating some momentum off one counter-attacking run, but the Kilkenny wingers, Rory Deverell and Keith Masterson, made their tackles, while their elusive out-half, Greg Jacob, and Armstrong made some inroads for their lively openside Niall Ryan to feed off.

Coached by a referee, Kevin Clayton, Kilkenny were considerably more disciplined at the breakdown. The spate of St Mary's transgressions ultimately earned Kilkenny a second close-in line-out. Second row Philip Ryan's take was also more cohesive and Niall Ryan's display was deservedly rewarded with the touchdown.

A lovely break by St Mary's out-half David O'Sullivan, and a close-range snipe by Stephen Hicks seemed certain to yield a pre-interval try but Kilkenny ran the turnover out from behind their own line. Despite Connolly kicking St Mary's ahead soon after the interval, Jacob's penalty drew Kilkenny level again.

after number eight Adrian Copeland, supported by Niall Ryan, and then Armstrong, made inroads off one of many clever line-out variations.

When a long-range penalty attempt by Connolly was run out from defence by Geoffrey Deane, Kilkenny were rewarded with an attacking line-out. Armstrong and the hard-running scrum-half Richard Jones in turn took play to the St Mary's line and from the recycle Copeland took Jones's blindside pass to crash over.

St Mary's appeared to have extricated themselves from defeat when Ciaran Potts cleverly released the ball for Richard Boyd to take Simon Nagle's pass and score.

Tellingly though, it was Kilkenny who probed harder for the decisive score. A daring counterattack by Jacob, running diagonally and feinting to pass before straightening through a gap, earned a penalty at the breakdown 36 metres out. Armstrong took aim and bisected the posts for a famous win.

Scoring Sequence: 10 mins: Higgins try 0-5; 31: N Ryan try 5-5; (half-time: 5-5); 37: Connolly pen 5-8; 42: Jacob pen 8-8; 49: Copeland try 13-8; 61: Boyd try 13-13; 71: Armstrong pen 16-13.

Kilkenny College: G Deane; R Deverell, C Peavoy, R Armstrong (capt), K Masterson; G Jacob, R Jones; G Roe, D James, B Thompson; J Kidd, P Ryan; K Stanley, A Copeland, N Ryan. Replacements: S Holland for N Ryan (54 mins), G Greene for Masterson (62 mins), E Young for Roe (69 mins).

St Mary's College: R Boyd; C Connolly, M Craig, S Nagle, I O'Herlihy; D O'Sullivan, S Hicks; K Rynhart, D Kilbride, M Wallis; E Higgins, C Queenan (capt); G O'Brien, D O'Brien, C Potts. Replacements: B McCormack for D O'Brien (44 mins), S Jennings for G O'Brien (49 mins).

Referee: M Whyte (Leinster).