This evening Bayern Munich host Barcelona and will have no option but to go out all guns blazing in an attempt to overturn their 3-0 defeat in the first leg at the Camp Nou last Wednesday. It’s a forlorn hope, but at least they have another shot at Messi & Co.

Tomorrow night, Real Madrid host Juventus in a more finely balanced affair, seeking to overturn their 2-1 deficit from the first leg. The two first legs were compelling matches, both tactically and technically, and probably exceeded any back-to-back night's football since or indeed including the World Cup.

Two legged semi-finals in the European Champions League are a rich part of the tournament’s history. Last week’s games demonstrate the importance of establishing a lead at home, but all the while both home and away sides are mindful there is a second leg to come. They are intriguing affairs, and they are also fair.

There is some argument that the team with the home tie in the second leg has a marginal advantage, especially if the second leg goes to extra time. But then again, as away goals count double, this is a negligible advantage if the away team scores in extra time.

In any event, it is as nothing compared to one-off semi-finals, where home advantage is determined purely by the luck of the draw. If the orchestrators of rugby's European Champions Cup – under the auspices of European Professional Club Rugby – really want to emulate their football counterparts, aside from not shoehorning the knockout stages into a five-week window starting a fortnight after the Six Nations, they could do little more to enhance the tournament than make the semi-finals two-legged.

Luck of draw

In the 20 years of the European Cup/Heineken Cup/European Champions Cup there have been 40 semi-finals, which have all been one-leg affairs where home country advantage was down to the luck of the draw. Of those 40 matches, the home team has reached the final 26 times and the away side 14 times.

In truth that doesn’t even paint the full picture as to how advantageous home advantage is in the semi-finals, for if one takes away the two drawn semi-finals (Brive advanced after a 22-all draw with Toulouse in the 1997-1998 campaign by dint of scoring more tries, and Leicester progressed by dint of winning a penalty shoot-out after a 26-all draw with Cardiff following extra time in 2009) the actual win-loss ratio would be 26-12.

One could go further and subtract the two Leinster-Munster derbies in 2006 and 2009, which both happened to be won by the away side in Lansdowne Road and Croke Park – very much neutral venues. Then the tally would be 26-10.

What’s more, of the 20 tournament winners, 13 had the advantage of a home semi-final; and take away those four previous examples, of the remaining 16 Cups, 12 of the eventual winners had the benefit of a home semi-final.

Admittedly, the sense of injustice is more acute on these shores, where the luck of the Irish hasn’t applied to the draw for the semi-finals.

Irish teams have made the semi-finals 21 times in total, but if one takes away those two all-Irish semi-finals in 2006 and 2009, of the other 17 occasions, the provinces have had six home semi-finals and been drawn away 11 times.

Of the 13 Irish-French semi-finals, the French club has been drawn at home in 10 of them. The provinces have won two of three at home, but lost seven of the 10 semi-finals away to French clubs. Munster have been drawn away in all seven semi-finals with French teams, winning twice and losing the other five.

In those seven cases the Irish teams have lost away to French clubs, the margins of defeat were one, one, 10, 11, six, eight and five points (and that was after Leinster had finished level with Toulon over 80 minutes). Imagine how differently those semi-finals might have panned out had the away side had the chance of overturning those far from insurmountable deficits in a second leg at home, and how fascinating those semi-finals would have been.

The same questions could be applied to this season’s semi-finals, in which case Saracens would only have had to overcome a four-point leeway in a return leg at home to Clermont, and Leinster would have started the second leg level.

Put another away, Toulouse have reached 10 semi-finals, and have been drawn at home in six of them. Of the four occasions they went on to lift the Cup, Toulouse were at home in three semi-finals. Of Munster’s 10 semi-finals, they have been drawn away eight times.

Reverse ratio

How much differently might history have panned out had the reverse ratio of home semi-finals occurred between the four- and two-time winners? Or if semi-finals had been conducted over two legs? Imagine if football’s European Champions League finalists had already been decided after one legged semi-finals, and it was now decided Barcelona would be playing Juventus in Berlin on June 6th?

The scramble for home advantage in the semi-finals in the Pro12 (where no away semi-finalist has ever reached the final in 10 attempts) or the Top 14 or English Premiership is altogether different. At least that is earned on merit by dint of final places that are achieved after a league campaign in which everybody plays everybody else home and away.

The luck of the draw at the semi-final stage has clearly distorted history, and the European Cup itself. It's just that we've got used to it. gthornley@irishtimes.com