The Mariners had lost their previous two A-League matches – last losing more in succession in a miserable 11-game stretch in 2020 – but Moresche made sure that short run came to an end.
The Brazilian did not get on the scoresheet himself but laid on the opener for Marco Urena after 13 minutes.
No player in the league has aimed more shots on target this season than Urena's nine, with his latest steered past Andrew Redmayne from Moresche's measured pass.
Three minutes later, it was two. Fine work from Lewis Miller on the right was followed by a low cross that sought out Moresche, only for Anthony Caceres to turn into his own net under pressure in front of the goal line.
Winless Sydney could not recover and extended its worst start to a season since 2010-2011, when it had to wait 11 matches for its first victory.