Northern Ireland face an uphill struggle to reach a first World Cup since 1986 after losing to Switzerland in controversial circumstances in the first leg of their play-off at Windsor Park.
Ricardo Rodriguez scored with a penalty just before the hour mark after Corry Evans was deemed to have handled inside the area.
Croatia capitalized on a dismal Greece defensive display to take a commanding lead after the first leg of their World Cup qualifying play-off in Zagreb.
Greek keeper Orestis Karnezis’ clumsy touch led to him conceding an early penalty, which Luka Modric converted.
Nikola Kalinic was unmarked to tap in a second but Sokratis Papastathopoulos’ fine header gave Greece an away goal.
Ivan Perisic headed Croatia’s third before half-time before Andrej Kramaric tapped in after a botched backpass.
Northern Ireland 0:1 Switzerland
Croatia 4:1 Greece