The Heineken Cup quarter-finals invariably throw up one surprise. Home advantage in the last eight counts for a lot, but not everything: in the 14 years of the competition, there have only been three years when no away side prevailed at the first knockout stage, all in a row from 1998-99.
Since 2002, there has always been at least one away quarter-final winner, as three of the four sides playing at home this weekend well know. Biarritz lost to Northampton in San Sebastián three years ago, Leinster were toppled by Munster the previous year and in 2005 Leicester comfortably defeated Leinster at Lansdowne Road.
Biarritz and Leinster were not strictly playing at home as they had moved grounds to attract a bigger crowd, as Leicester did in 2006 when they took their quarter-final against Bath to the Walkers Stadium and lost 15-12. Biarritz are back at Estadio Anoeta in San Sebastián on Saturday where they will face the Ospreys, their fifth Heineken Cup knockout tie at the ground.
They won three before Northampton, in the year they were relegated from the Premiership, caused one of the biggest upsets in the tournament's history. Biarritz were then bogged down by a playing style that was more stereotypically English than French – rarely taking risks and kicking for position.
They have since rediscovered some of their swagger and in the United States wing, Takudzwa Ngwenya, they have one of the most dangerous finishers around, but they were hardly in the most taxing group this season and their record in the Top 14 is 50% after 24 rounds of matches. They lie seventh in the table with two games to go, three points off the play-off places with their next match against the team immediately above them, and the only one they can overhaul, Racing Métro.
Lose that and Biarritz, or another French club, will probably have to win this season's Heineken Cup for the Basque club to qualify for next season's tournament. While they have been strong at home, they have won only two league matches on the road, even managing to lose to relegated Albi a couple of weeks after becoming the first, and so far only, side to win at Clermont Auvergne.
The Ospreys are hardly more consistent and while this is the third consecutive season that they have made the quarter-finals, they went down with a whimper in Munster last year having failed to live up to their tag of favourites in 2008. Yet San Sebastián would appear to be the most likely venue for an away win.
If Biarritz brim with quality, from Ngwenya, Damien Traille and Dimitri Yachvili, to Fabien Barcella, Jérôme Thion and Imanol Harinordoquy, the Ospreys can field a team of full internationals and have many more on the bench. Like Leinster a year ago, they are looking for their breakthrough game in Europe: it came for the Irish province at Harlequins, Bloodgate and all, and now it is the Ospreys who have to stoop to conquer.
Ordinarily, Munster would be the home team to back not to lose a quarter-final. They have only ever lost two Heineken Cup matches on their own turf and just once at Thomond Park, and they beat Saturday's opponents, Northampton, there at the end of January.
The Saints wasted an opportunity that day, not least when they had an attacking scrum with Paul O'Connell in the sin-bin only to be twisted off the ball. Such moments define close matches and Munster had looked fallible up front until then.
Munster have been written off before, but they lost at home to Leinster last week and Northampton have won 19 of their last 21 matches in all competitions. The question is whether the Saints will handle the occasion better than they did 11 weeks ago, although they knew that night that a point would be enough to take them into the last eight.
Shane Geraghty started that night and, unlike the first meeting between the sides at Franklin's Gardens when he darted and dazzled, was a frazzle of indecision. He has not been first choice at Northampton since and would, perhaps, have been better served staying at London Irish last summer, not that anyone would have said that last October.
The other two quarter-finals would seem more straightforward to call. Leinster top the Magners League and have lost only once at home this season, to London Irish on the opening weekend of the Heineken Cup. Clermont Auvergne have won four out of 15 on the road this season, although Toulouse were among their victims.
Toulouse entertain Stade Français on Sunday having won 29-0 in Paris last month. Stade did draw in Toulouse last September but their season has been so wretched that they have little chance of making the Top 14 play-offs. An attraction of cup competitions is that form is not always the key: expect the unexpected.
This is an excerpt from The Breakdown, guardian.co.uk/sport's free rugby email. Get The Breakdown delivered direct to your inbox by signing up here. Paul Rees will be writing The Breakdown for the rest of the season.
