The reigning Olympic gold medallists shrugged off the USA in a superb performance, winning 11-6.
After a shaky start to the London 2012 Games - with two defeats and two wins - the nine-time gold medallists looked back to their best with a ruthless win over the Beijing 2008 runners-up.
The victory puts the Hungarians ahead of the USA in Group B.
Their defensive display stopped their opponents finding the back of the net, while at the other end their accuracy and efficiency in front of goal was merciless.
Norbert Hosnyanszky blasted a hat-trick for the Hungarians, while captain Peter Biros netted two.
Adam Steinmetz, Norbert Madaras, Tamas Varga, Marton Szivos, Gergely Kiss and Tamas Kasas scored one apiece.
Elsewhere, Serbia cruised past Romania to win their group.
They hardly needed to get out of second gear as they brushed aside their opponents 12-4 to remain unbeaten in the competition.
The Beijing 2008 bronze medallists and European champions came into the Olympics as favourites, and their form will worry the other teams in the quarter-finals.
Serbia will play Australia in a quarter-final clash on Wednesday, and the Australians had the ideal preparation, as they beat Greece to book their last-eight spot.
Australia went behind in the opening minutes of the contest, but strong second and third periods gave them a well-earned win and a place in the knockouts.
In the first game of the day, centre forward Niksa Dobud scored six of the best for Croatia as they powered past Kazakhstan 12-4 to maintain their 100 per cent record.
The in-form side had already guaranteed top spot in Group A and a place in the quarter-finals, but their record of five wins from five matches sends a strong message to their rivals.
Later in the Water Polo Arena, Italy beat Spain 10-7 to clinch second place in Group A while Montenegro eased past Host Nation Great Britain, 13-4.
Aleksandar Radovic and Boris Zlokovic scored hat-tricks for Montenegro, while Mladan Janovic and Aleksandar Ivovic netted a brace each.