Guaranteed winners in tomorrow's second Bank of Ireland All-Ireland semi-final are the GAA, who expect a sell-out.

After an amount of concern that last year's massive crowds at the new Croke Park owed more than is comfortable to the presence of Dublin, the authorities will be immensely gratified that attendances at the semi-finals of this year's football championship are actually up on 12 months ago.

The match also represents a big turnaround for Donegal whose supporters were outnumbered about four to one in last year's capacity quarter-final replay with Dublin but whose supporters have been devouring tickets all week for tomorrow's tilt at the champions.

It's safe to speculate that Armagh manager Joe Kernan would have preferred to see Galway coming at his team in this match. They owe the Connacht champions after the one-point defeat of two years ago and could have been relied upon to turn that background into a crusade.

But there's no such slight crying out for vengeance in the background to this weekend. The two counties have a largely harmless history having met in two Ulster finals, including last year, and won one each.

That meeting 13 months ago is of direct relevance to this weekend with 80 per cent of the same personnel on duty. So - strangely enough given the often feud-strewn landscape of Ulster football - neither side have any particular axe to grind with the other.

Yet Donegal are an Ulster team. This summer has seen the emergence of a mystique about Armagh, which seems to be particularly potent among the other provinces.

This weekend's opponents and their manager Brian McEniff, who has been in charge of Ulster's Railway Cup team since old God's time, are unlikely to be similarly impressed.

McEniff's achievement this year has been immense. In the first year of each of his previous management stints he won the Ulster title. This year he didn't but has once more brought the county to Croke Park for an All-Ireland semi-final - at least as memorable a feat in these days of qualifiers.

What are we to expect on the field? Who knows after last week's theoretically gourmet clash of contrasting styles turned into something so indigestible? With two men up and blanket defence all around will there be anyone there for the throw-in? It is easy to caricature the teams but there have been few complaints about the entertainment value of most of the matches involving Armagh and Donegal to date. McEniff described his team's defeat by Fermanagh as a low point in the county's history but otherwise they have scored well and possess in Adrian Sweeney and Brendan Devenney a double act well worthy of slugging it out with the efforts of Steven McDonnell and Diarmuid Marsden.

They're as adept as Armagh at crowding the middle and dropping men back and their defence will swarm with the best of their opponents. In the end the match will come down to who is better and there are a couple of reasons for believing that the champions should win on that basis.

In last year's Ulster final Armagh were in difficulties for much of the match before finishing it out in now familiar style for a four-point win. Yet despite Donegal's display that was Armagh's second easiest win in their eight-match campaign last year with the only the devastation of Fermanagh ending on a bigger margin.

In other words Donegal's failure to take chances meant Armagh won well. The champions' attention to defensive detail will reduce the number of chances Donegal create.

Secondly, a point made by John Morrison, Mickey Moran's assistant in Derry and in Donegal last year, deserves repetition. Armagh's forwards, he said, can work with bad ball and improvise when things aren't going well. This economy on the ball and with it makes McDonnell, Marsden and company far more lethal adversaries that a misfiring Galway were on either occasion.

There is much for Armagh to fear about Donegal. McEniff knows them inside out and has created a momentum that won't be easily halted. Donegal are also a side that won't regard the final 10 minutes as exclusively Armagh's opportunity to shine.

But ultimately Donegal don't have the same scoring options as Armagh and when matches are tight that is a fatal hindrance.

The GAA has asked supporters to note that it is now unlikely there will be any tickets available or on sale tomorrow. Admission will be by ticket only.