Belgium reached their first World Cup finals since 2002 after on-loan Everton striker Romelu Lukaku scored two excellent individual goals in the first half to earn a 2-1 victory in Croatia on Friday.
The result means Group A leaders Belgium are uncatchable with 25 points from nine matches ahead of their final qualifying game at home to Wales on Tuesday.
Lukaku, on loan to Everton from Chelsea, had several thousand Belgian fans dancing on the half-empty terraces at the Maksimir stadium after scoring in the 15th and 38th minutes.
"I'm super happy for the team. We always believed we could qualify and now it's here," Lukaku told Belgian television.
I'm super happy for the team. We always believed we could
qualify and now it's here
Victory on a wet night in Zagreb prompted joyous celebrations from the Belgian players in front of a sizeable and vociferous contingent of travelling fans.
Second-half substitute Niko Kranjcar grabbed a late consolation goal for the Croatians.
The home team have 17 points and are assured of a runners-up finish and a berth in next month's playoffs but were jeered by their fans after a lacklustre performance.
Croatia needed a win to have any chance of overhauling Belgium at the top but coach Igor Stimac deployed a conservative 4-5-1 formation with wingers Ivan Perisic and Ivan Rakitic operating behind lone striker Mario Mandzukic.
The visitors took the lead when Perisic gave the ball away to Steven Defour who fed Lukaku and he raced clear of centre backs Vedran Corluka and Dejan Lovren before rounding keeper Stipe Pletikosa.
Pletikosa then kept out a close-range header from Marouane Fellaini but could not prevent Lukaku scoring a dazzling second goal.
Having superbly dinked the ball over Lovren inside his own half, the 20-year-old galloped past midfielder Mateo Kovacic, rounded the advancing Pletikosa and walked the ball into an empty net as bewildered home fans started leaving the ground in droves.
Belgium almost scored a third goal in the 77th minute when Pletikosa denied Fellaini from three metres after a darting run and cross by Eden Hazard.
Kranjcar pulled one back for Croatia by volleying a fierce shot into the roof of the net from 14 metres after keeper Thibaut Courtois parried a close-range effort by Nikola Kalinic and Daniel Van Buyten could only partially clear the rebound.
Elsewhere, Bulgaria's hopes of securing second place behind Italy in Group B, and a potential playoff match, suffered a huge setback after they had two players sent off in a 2-1 defeat in Armenia with the hosts netting the winner three minutes from time.
The Bulgarians had Nikolay Bodurov dismissed on the stroke of halftime and went down to nine men after 63 minutes when Svetoslav Dyakov was shown a second yellow card.
Yura Movsisyan won it for Armenia when he broke clear to score late on.