Russia overcame Italy to announce their intentions for a medal.
After a cagey first half, the World Championships bronze medallists pulled ahead in the third quarter and a late Italian fightback was not enough to bother them.
They now have a 100 per cent record in Group B, after beating Great Britain narrowly in their last game.
Russia scored first to lead at the end of the first quarter 1-0. They doubled their tally in the second period, but Italy pegged one back before half time.
The Russians stepped up a gear to win the penultimate quarter 4-1 to put daylight between them and their opponents.
An Italian late charge saw them win the fourth quarter 2-1, but the match finished 7-4 to Russia.
In Group A, Spain and USA held each other to a 9-9 draw.
Both sides were looking to build on winning starts, but they shared the spoils after a tense encounter at the Water Polo Arena.
Spain dominated the first half, while their opponents fought back in the second. The Spanish powered to a 3-1 lead after the first quarter, and held the two-goal cushion going into the half-time break at 5-3.
The USA flew out of the blocks in the third quarter to claw back the deficit, before a Spain goal restored their lead to 6-5.
They had a fantastic chance to pull away, but captain Jennifer Pareja fired a penalty into the arms of the USA goalkeeper, and the USA capitalised by scoring again at the other end to level the scores at 6-6.
Another USA goal gave them the lead for the first time with a minute on the clock in the third period, and the quarter finished 7-6 to the USA.
Spain edged the fourth quarter by one goal, bringing the score to 9-9 at the final whistle.
Hungary snatched victory from China in a thrilling clash, edging ahead for the first time with less than two minutes to go before clinging on to win 11-10.
China were ahead for most of the Group A encounter, but Hungary were never too far behind, and pounced on their opponents in the closing minutes.
In the final game of the day, Australia recorded a big win, 16-3 against Great Britain.
The Australians led from start to finish, dominating in every area of the game to see out a comfortable victory.