A gripping tie was locked at 2-2 after extra-time before United took it out on penalties against the NPL ladder leader.
But, at the other end of the spectrum, ambitious start-up club Sydney CBD's fairytale faltered as it was beaten 3-0 by Woonona at Valentines Sports Park.
NPL early-season struggler South Coast Wolves suffered a scare before overcoming lowly ranked Mt Druitt Town Rangers 3-2 thanks to a late goal by Peter Simonoski at Popondetta Park.
High-flying Bonnyrigg White Eagles was given a stern test as it edged past Fraser Park FC 3-2 at Parside Park in an entertaining tussle.
And Parramatta Eagles was pushed to the limit by Southern Bulls, winning 5-4 on penalties at home after the game had finished 3-3 after extra time.
Port Kembla won 4-0 at Carlton, Rockdale City eased to a 2-1 victory at Rydalmere FC and Bulli put Bonnet Bay to the sword 11-1, with Sydney Uni eclipsing Albion Park 4-3.
Meanwhile Hakoah FC, which enjoyed a stunning cup run last season, began its campaign with a 2-1 win over Glebe Gorillas.