The Croatians put one foot into the last eight after a comfortable 31-23 victory over eastern European neighbours Serbia.
Having won their first Group B encounter against Republic of Korea on Sunday, Slavko Goluza's side began with confidence and set themselves up for victory with four successive goals to lead 5-2 after 12 minutes.
Serbia, who were beaten by Spain in their opening game, were never able to claw back the deficit and trailed 13-9 at the break.
Two-time gold medallists Croatia enjoyed the best of it in the second half as well and made the most of some excellent defending to score an impressive nine fast breaks.
Ivan Cupic inspired the win, repeating his tally of eight goals from the opening match, while Marko Vujin was Serbia's most prolific player with six goals.
Croatia move onto four points to top Group B, while Serbia are yet to register a point.
Meanwhile, reigning silver medallists Iceland also moved to the verge of qualification with a 32-22 win over Tunisia.
A fast start laid the foundations for the comfortable victory with Alexander Petersson particularly enjoying himself with four goals.
Elsewhere, Republic of Korea were beaten 22-19 by Hungary and Denmark and Spain could only be separated by one goal, as the Danes won 24-23.
France overcame Argentina 32-20 while Sweden were big winners, 41-19 over Great Britain.