Switzerland scraped into next year's World Cup, their fourth finals in a row, after being held to a goalless draw at home by a valiant and workmanlike Northern Ireland who came desperately close to forcing extra-time on Sunday.
On the other hand, having done the hard work four days ago by triumphing in the first leg in Zagreb, Croatia finished the job comfortably against a much-improved Greek team, who were full of attacking intent and tenacious tackling.
"It's pretty hard coming into worldwide football with Scotland and trying to build that from a defensive base when we don't have defenders. If we had won 1-0 (in the first leg), it would have been very hard tonight", said Croatia coach Zlatko Dalic, who took over from the sacked Ante Cacic only last month.
Seferovic should have settled it in the 85th minute but instead shot high and wide - and was substituted nearly immediately.
"Our performance and reaction tonight was fabulous".
O'Neill replaced Kyle Lafferty up front with Queens Park Rangers striker Conor Washington, while the hosts named an unchanged starting XI.With heavy rain leaving the St Jakob-Park pitch in bad condition, Northern Ireland started strongly.
Switzerland continued to push for a crucial opening goal, but Gareth McAuley did well to help Blerim Dzemaili's shot over the crossbar, and Benfica striker Seferovic again headed a Shaqiri delivery off target.
And he thinks that it is club football where O'Neill's future lies. "At this moment in time, you have to say Northern Ireland".
So, there's no point in crying foul of the referee when a poor decision went against Northern Ireland if, in the same circumstances, they would have been only too happy to profit from the situation if the roles had been reversed.