Should they have to make the return cross-border journey home with nothing to show for their trouble, and the Ospreys and Munster both win on home soil, Leinster will be out. In that worst-case scenario, not even the most miraculous of mathematical equations will save them.
The old adage about sport being a matter of inches has rarely been more vividly illustrated than Leinster's valiant effort to knock Toulon out of the European Champions' Cup. There were two minutes and four seconds left on the clock when Gopperth's drop missed by no more than a foot or two.
Had it gone over, Leinster would surely have spared themselves and their admirers the anguish of extra-time. The same could be said of Ian Madigan's penalty which rebounded off an upright some ten minutes earlier. The ricochet could just as easily have bounced over.
The more rarefied the atmosphere close to the summit of the European game, the shorter those inches become. Had Leinster gone through 15-12 in normal time, Toulon could not have complained.
Mourad Boudjellal, the holders' president whose lavish backing has been rewarded by making his club the first to reach three successive finals, does not need to be told how close his global collection of superstars came to losing their crown. He estimated the gap between Gopperth's near-miss and Toulon's exit at five inches.
Having seen their opponents finish on the wrong end of the closest of close-shaves, Ulster will be braced for the latest defence of an unbeaten home record in the GUINNESS PRO12 which stretches back over 12 months since the last time they lost before their own fans, on May 2 last year.
And guess who beat them? Leinster, 22-20 despite yellow cards for Rob Kearney and Rhys Ruddock. And, just for good measure, they proceeded to beat Ulster again a fortnight later, 13-9 in the play-off semi-final at the RDS Arena.
A sell-out crowd of some 18,000 will provide raucous proof of the enduring appeal of a fixture first played 140 years ago. Ulster's GUINNESS PRO12 attendances have been soaring on an upward curve all season - 16,260 against the Warriors last October, 17,107 against Connacht on Boxing Day, 17,138 against the Scarlets in February and now the biggest one of all.
With six wins from their last seven in the GUINNESS PRO12, Ulster must make it seven out of eight if they are to clinch a home semi-final. Darren Cave, the province's much-admired centre, gives some idea of his squad's desire to go all the way and ensure they are there for Belfast's first GUINNESS PRO12 Final on May 30, already a sell-out.
"My first season was 2006-7 so it's a long time to have been here with nothing to show for it really," he says.
"There are some great memories and a couple of medals that are the wrong colour. I believe in this team. I said when Ireland renewed my contract that the coaching set-up we have now is the best I've experienced at Ulster."
Munster, ahead of them in second place on points-difference, will expect to make the most of Saturday's match in Cork against Benetton Treviso, without a win outside Italy since they walloped the Scarlets 41-17 two years ago.
The biggest crowd for the rugby weekend, bigger than anything in the Aviva Premiership or the Top 14, will be at the Millennium Stadium in Cardiff for the four regions' annual double-header - Judgement Day III.
It has already broken box-office records with ticket sales topping 40,000. The Ospreys, two points behind Ulster and Munster in fourth and therefore in striking distance of a home semi-final, cannot afford to slip up against the Blues, back in Cardiff for the first time since their 88th minute win over Connacht seven weeks ago. The Blues and Ospreys kick off at 2.30pm followed by the Dragons and Scarlets at 4.45pm.
The Warriors, still out in front where they have been for most of the season, appear in Galway on Saturday without two of their international backs, Scotland centre Mark Bennett, out for the rest of the season, and Canadian wing DTH van der Merwe, who may or may not be back next month following wrist surgery.
Connacht, despite a run of three straight defeats, are still sixth but only by virtue of points-difference above the Scarlets. Edinburgh, one point behind in the three-horse race to secure the last Champions' Cup place, welcome Zebre to BT Murrayfield in buoyant mood after their historic performance last week.
A thumping home win over the Dragons ensures that Scotland's capital team will fly the GUINNESS PRO12 flag in the European Challenge Cup final against Gloucester at Twickenham Stoop on Friday May 1.
As the first Scottish team to reach a European final, they will not lack for any motivation against Zebre, having lost to the Italians last November.
The five play-off contenders and their composite GUINNESS PRO12 record over the last four seasons, excluding play-offs and Finals, show Leinster and the Warriors with identical records.
| TEAM | PLAYED | WON | DRAWN | LOST | FINALS |
| Leinster | 85 | 61 | 5 | 19 | 5 |
| Warriors | 85 | 61 | 5 | 19 | 1 |
| Ulster | 85 | 57 | 2 | 26 | 1 |
| Ospreys | 85 | 56 | 4 | 25 | 2 |
| Munster | 85 | 54 | 3 | 28 | 1 |
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