Westmeath v Derry: Writing previews on the championship this year has become a hazardous task. Still, the gut feeling is that today's opening act in Croke Park will edge towards the best defence. Recent evidence has proved a poor reference point, but Westmeath have been tighter far.

Both sides have their rocks at full back - Donal O'Donoghue and Niall McCusker - while Westmeath's (stick-like-glue) corner back John Keane has been one of the unassuming stars of the championship.

Derry counteract this by welcoming back one Seán Marty Lockhart after a prolonged absence with a leg infection. Lockhart also takes over the captaincy from Paddy Bradley and will be commissioned to silence Dessie Dolan, with Keane keeping tabs on the free-scoring Bradley (1-30 so far this year).

Significantly, Bradley comes into the game with doubts over his fitness.

Westmeath full forward Denis Glennon lived up to his early-season billing with a four-point haul in the drawn Leinster final against Laois, and followed that up with a brace in the replay - all from play.

The only problem is the teenager's skills are no longer a secret. Alan Mangan is another handful, as is Derry's Enda Muldoon, so it's just a matter of who can sustain form for 70 minutes.

With so many talented players cancelling each other out around the square, this contest could well be sorted farther outfield. In Johnny McBride and Conleth Moran, Derry appear to have the better half-forward line, but that may prove pointless if the supply line is cut in the middle.

Westmeath have become masters at picking up the loose balls in the middle third but that is a battle normally won by the hungrier side.

This sets everything up nicely for Rory O'Connell to further frustrate the GAC. Although he was hit with a 12-week suspension after being sent off against Offaly in the Leinster championship, a High Court injunction ensured he picked up a Leinster winner's medal with his colleagues last month.

After an early introduction in the drawn encounter and a full match in the replay, O'Connell is nearing full tilt.

Fergal Doherty and Patsy Bradley have the football challenge of their careers to stem the dominance of O'Connell and captain David O'Shaughnessy.

But bet against Derry at your peril. Like Fermanagh, they have been hardened by the qualifiers. Given they are the only two northern counties still in the mix, comparisons between them are inevitable.

Both sides are supposedly in transition as Fermanagh lost a wealth of talent, while Derry said farewell to the midfield institution that was Anthony Tohill.

Also, their sharp-shooting forwards have been finishing matches with a spring in their boots, Derry's 10 points without reply against Cavan in round two being the best example.

Yet, their collapse against Tyrone compares poorly to Fermanagh's tight contest with the All-Ireland champions. Also, the Ernesiders have been in far tougher battles than Derry's run against Wicklow, Cavan, Wexford and a worn out Limerick.

As have Westmeath. Getting over all those historical barriers leaves them with a clear path to further glory. In the immediate aftermath of victory over Laois, Páidí Ó Sé assured the galleries his team would not limp away with a shabby performance in the All-Ireland series.

The proverbial shackles are now loosened, making the All-Ireland a realistic goal.

Derry will be expected to last the pace but since beating Cavan every further step has been a bonus.

However, if they come in with a similar mindset to that of their fellow Ulster giant-killers, anything seems possible.

And yet, Westmeath should progress so long as the Derry witch doctors and shamans have not been in fruitful consultation with Charlie Mulgrew and company this week.