IT'S the oldest cliché in the book but resonates strongly any time Tyrone and Derry cross swords- 'form really does go out the window'.

After quashing the challenge of one of their fiercest rivals in the opening round three weeks ago, Mickey Harte's team continue their quest for a 12th Ulster title and more significantly back-to-back All-Irelands, against their other principal historic foe this Sunday afternoon at Casement Park.

The Oak Leafers will relish the underdogs tag. They revelled in their party pooper role just three years ago in Omagh when the counties last collided in the Championship.

Then as now, Tyrone entered the contest as reigning All-Ireland champions, but after the highs of '05, Healy Park on May 28th 2006 provided some excruciating withdrawal symptoms.

Held scoreless in the first half, Tyrone eventually succumbed 1-8 to 0-5. It was the ultimate cold turkey for those still pumped on the adrenaline charge of the previous campaign.

A spot in the Ulster Final on July 19th is the immediate reward at stake for this Sunday's victors but building on the momentum garnered from that promising first Championship outing of the summer is just as important for the Red Hands.

Tyrone did what they had to do against Armagh and while the contest probably lacked the physical intensity and ferocity that we have come to expect from previous encounters between the teams, nonetheless the manager will have gleaned much satisfaction from the contest.

On the surface this Sunday's semi should follow the 'fire and brimstone' script we normally associate with meetings between Ulster's heavyweights in the Championship, yet Derry's approach will be interesting given the severe criticism aimed in their direction after their first round skirmish with Monaghan.

The disciplinary chiefs came down heavily on the respective counties after that unseemly spectacle, with Derry duo Brian Mullin and captain Fergal Doherty both picking up suspensions.

Those well-publicised sanctions and the general attitude of either set of players dominated the airwaves and newsprint in the aftermath of the fractious Celtic Park contest and the scale of the publicity may deter Damian Cassidy's troops from adopting similar tactics this weekend.

Such a gameplan, however ugly, worked a treat back when Paddy Crozier was at the helm in '06. Both teams were roundly criticised for the poor quality exhibited, the victors Derry in particular shipping plenty of flak for the spoiling tactics and persistent fouling which frustrated the Tyrone players.

Nonetheless it would be surprising if the Oak Leafers risk the wrath of the authorities again so soon after their 'Farney frolics' which augurs well for a more pleasing spectacle on Sunday. Perhaps!

The last time that Tyrone succumbed to Derry in the Championship they were slammed for being bereft of inspiration, leadership and most importantly attacking potency. Such shortcomings though shouldn't be a concern this term based on the evidence of their Clones showing three weeks ago.

The likes of Ryan McMenamin, Davy Harte, Philip Jordan, Justin McMahon and Enda McGinley essentially picked up where they left off last autumn with diligent, disciplined and at times dynamic performances, mostly in a defensive capacity.

Add in a rejuvenated Eoin Mulligan, Stephen O'Neill's encouraging return to the Ulster arena and captain Brian Dooher's sparkling cameo and its difficult to temper expectations as to what could lie in store in the weeks and months ahead. (And that's without even mentioning 2008 Footballer of the Year Sean Cavanagh and the convalescing Brian McGuigan).

Tyrone only shifted through the gears on a sporadic basis at St Tiernach's and while it might be argued that Armagh are a team in transition, they would still be regarded as one of the top eight forces in the country.

However past reputations count for little on Ulster's mean streets and no doubt success starved Oak Leaf players and supporters now want a slice of the glory themselves.

They will derive some encouragement from Tyrone's unease for a 15 minute spell during the second half of the Armagh match when an isolated full-back line struggled to quell the physical threat of Clarke and Steven McDonnell once the Orchard men employed a more direct approach.

The Bradley brothers, Paddy and Eoin, as well as emerging young gun James Kielt (if fit), would be confident of exploiting such vulnerabilities if repeated, though it will be surprising if the Tyrone half-backs leave their defensive colleagues quite as exposed again.

Undoubtedly Tyrone took their foot off the pedal when Conor Gormley rammed home that early second half goal, which stretched their advantage to eight points against a struggling Armagh team, and what ensued should act as a salutary lesson of the need to guard against complacency.

The manner in which the All-Ireland champions ended the encounter however also underlined their maturity and confidence. A couple of superb scores, after measured approach work, helped quell the Orange fightback and spoke volumes for Tyrone's all round pedigree and self-belief. 'They just don't do panic', as Pat the Puke once commented.

That 2006 triumph in Omagh proved to be something of a false dawn for Derry who are still craving their first Ulster title since 1998. Unlike Armagh, a provincial breakthrough would represent a massive achievement for them after spending a frustrating decade living in the shadows of their neighbours from across the Sperrins.

Consistent showings in the league in the springtime haven't translated into tangible reward once the Championship comes around in the summer.

Premature exits have perennially given way to recriminations and post-mortems, a cycle of failure which their former All-Ireland winner Cassidy is intent on ending.

He has helped heal the various rifts within the camp and brought a tactical nous to the set-up which perhaps has been missing in the past.

Both Sunday's combatants may have avoided a potentially treacherous first round Qualifier tie with their respective provincial Quarter Final victories, but that only amounted to a stay of execution for one of them.

The defeated side will be tossed through the 'back-door' with all the other early losers and face a long hazardous 'summer of Saturdays' if they are to re-emerge as genuine All-Ireland contenders in early August.

One senses it's the nightmare scenario for Derry who won't harbour any genuine aspirations of lifting 'Sam' at this juncture under Cassidy's stewardship and have concentrated their thoughts solely on the Anglo-Celt.

Yet while Tyrone are more likely to be able to regroup, a Championship defeat to their fierce rivals would still be hard to stomach, particularly given the galling loss suffered to the same opposition three years ago.

The league meeting back in April at Healy Park when the hosts took the spoils would suggest that there is still considerable daylight between the two counties and that was a Tyrone panel without a number of its big hitters.

The Red Hand juggernaut looks to be gathering steam again... but then we thought the same in '06.