Northern Ireland stunned by Estonia drubbing
The hosts, who are in contention to make the play-offs, broke the deadlock on 28 minutes when Martin Vunk ran in to fire home from the edge of the area from a deflected cross.
Estonia were gifted a second goal four minutes later when Tarmo Kink left fly from 30 metres with a dipping shot that completely deceived keeper Lee Camp.
It was then the hosts turn to lay on a goal for the visitors, Raio Piiroja heading into his own net shortly before the break.
Northern Ireland's hopes of a further comeback were jolted by more slack defending on 59 minutes, Gareth McCauley failing to clear in front of goal and allowing substitute Sergei Zenjov to nip in and score.
Fellow substitute Kaimar Saag rounded off a convincing win with a fourth goal in stoppage-time.
Italy have qualified automatically as group winners, leaving Serbia (14 points), Estonia (13) and Slovenia (11) battling for a play-off place.