Not for the first time this season, Adelaide United are up against it.Top of the A-League on goal difference ahead of the fast-finishing Melbourne Victory, the Reds must better their Victorian rivals' result at home to Wellington on Friday night in order to lift the premiers plate.They will have to do so against the Central Coast Mariners, who like Melbourne have been unbeaten against Adelaide this term.The Mariners' attack has troubled United this season, scoring six goals in their two meetings so far - the first an extraordinary 3-3 draw at Hindmarsh when the home side squandered a 3-0 advantage.Adelaide's back four may well be in for another unhappy night given that defensive cornerstone Sasa Ognenovski is suspended following his fifth yellow card of the season, in New Zealand last week.Injuries to Alemao (groin) and Jason Spagnuolo (knee) further complicate matters, though there is the advantage of Cassio's return after missing last week to be with his wife as she gave birth.When put together the scenario is the sort to furrow any coach's brow, but United boss Aurelio Vidmar said it was near miraculous that his team were even in the position they presently occupy after their adventures in the Asian Champions League and Club World Cup."It's been tough, really tough, you don't understand how difficult it's been to play on three fronts," he said on Friday."It's been really tough, so for us to be in the position we're in today it's amazing."The effort they've put in from day one to get to this point has been nothing short of a miracle really."Thrown into the mix too is the fact that numerous players now know they will not be at Hindmarsh beyond the finals series, with a high player turnover set to break-up much of the squad that forged a historic path through Asia in 2008-09.Vidmar's energies have been diverted somewhat by the race for signatures, particularly since Ognenovski elected to pursue a more lucrative career path in Korea."Two weeks ago Sasa was an Adelaide United player, we brought in Fyfey (Sydney FC's Iain Fyfe) and didn't have a problem with our defence ... now that has changed, the whole dynamic," Vidmar said."We missed out on a couple players earlier on, now that Sasa's gone we have to look again."With all that complexity to worry about, the Reds are grateful to be playing last this weekend, meaning they will know exactly what must be achieved when they turn out against the Mariners in Gosford."You don't know what's going to happen, there are probably 1000 permutations between tonight and Sunday, so we need to wait and see what happens with Melbourne," said Vidmar."(But) by the time we play on Sunday everything else will be sorted out, so we'll know exactly what we need to do."