Greece topped Group C in front of defending champions United States as the opening round of matches concluded at the International Swimming Federation (FINA) World Women's Youth Water Polo Championships in Auckland.
The Greeks and the Americans drew 10-10 yesterday with only the group winners guaranteeing a place in the quarter-finals.
The Americans did their part with a 14-7 victory over third-place China, leaving Greece needing victory by 17 goals to leap-frog them at the summit.
They duly obliged with a rampant 27-9 victory at the Sir Owen Glenn National Aquatic Centre in the New Zealand city.
It means the US will have to play-off to reach the last eight, with all second and third place teams given an extra chance to progress.
In Group A, Russia topped the pile with a 100 per cent record.
They recorded a 16-6 win over New Zealand which handed the Kiwis a second defeat and meant they finished third.
Spain will enter the play-offs after finishing behind Russia in second, thanks to their 19-3 victory over winless South Africa.
Group B, which features just three teams, was won by The Netherlands who made it two wins from two with an 11-9 success over Australia who have recorded two defeats.
The match was level until the final four minutes with the Dutch prevailing despite the Australians leading twice in the contest.
Italy, who were not in action today, finished second thanks to their earlier success over Australia, who will also enter the play-offs despite losing both of their games, due the group consisting of three teams.
In Group D, Hungary topped the group in front of Canada with both teams finishing on five points.
The Hungarians thrashed third-placed Germany 17-5 to win the group on goal difference.
It meant Canada's big 19-4 win over Mexico was only good enough for the play-offs, which will take place tomorrow.
The US will meet Germany, with hosts New Zealand playing Italy.
Spain face Australia and China play Canada.
The US beat Canada 5-4 in the final of the last edition, held in Spain's capital Madrid in 2014.