Northern Ireland boss Michael O'Neill maintains his players still believe they can reach Russia and will not dwell on the penalty decision that could scupper their World Cup dream.
It is Switzerland who are currently on course to emerge from the play-offs with a finals ticket, having won 1-0 in Belfast thanks to a dubious penalty that still stings Northern Irish fans.
The team trained in Basel on Saturday night without Stuart Dallas, who picked up a foot injury on Thursday, and is rated a major doubt for Sunday's fixture, live on Sky Sports Football from 4.30pm.
O'Neill insists his players are concentrating on overturning the deficit rather than stewing over referee Ovidiu Hategan believing Corry Evans handled Xherdan Shaqiri's shot.
"There's a lot of emotion in the dressing room after the game which is natural - but it's gone now," O'Neill said.
"What happened in the game, we have to take motivation from it, but it's gone now in terms of where it is in the players' mind and the focus is on trying to get the result that could take us through.
"I said to the players on Friday what's happened has gone, we've got to leave it behind, it's not something we need to dwell on. Our focus is on what lies ahead, and not the officials."
Overcoming their position to qualify will be a tall order given Switzerland have won nine competitive games on the spin at home and England are the only team to have won a qualifier on Swiss soil since 2008.
No European team has ever advanced through the play-offs after losing the first leg at home and the Northern Irish have now suffered three defeats in a row - to Germany, Norway and Switzerland, scoring just once in that time.
However, O'Neill insists his players are not mentally shot.
"I don't think they're short on confidence, I don't think they're short on belief," he added.
"It's different from qualification because Switzerland have been to the last 16 of the last two major tournaments. It lifts the level from qualification and we have to get to that level. That's the challenge.
"There's still a lot of confidence and belief in the group that they're capable of coming here and making things difficult for Switzerland, and hopefully we get the result that we are after."