Caversham's sharpshooters had already beaten Dunedin Technical 5-1 and Mosgiel 8-0, and it was Roslyn's turn as Caversham racked up 21 goals in three cup ties, suggesting an immense gulf exists in local football.
Roslyn started with a hiss and a roar, pressurising Caversham into error, and after only five minutes a convincing penalty shout was waved away by referee Dave Langley.
Caversham responded as it usually does, with slick passing, genuine pace in attack and confident commitment of numbers forward.
The stocky Ant Hancock scored after 19 minutes from a Harley Rodeka right-wing cross, and less than a minute later Tom Jackson scored the first of his hat trick of goals.
Roslyn continued to battle and won a fair share of possession, but the ethereal running of Tim Dalman typified a Roslyn attack that lacked real substance for most of the match.
Tim Mather's stability initiated some promising attacks; Tom Connor, Sam Mepham and James Watson earned hard won possession and Dave Shaw and Brad Johnstone anchored the defence but, on the day, Roslyn lacked menace.
In contrast, coach Steve Fleming's Caversham played with cavalier style.
Patrick Fleming showed excellent technique, pace and finishing power.
He found space, made telling passes and, when required, tackled with gusto.
Roslyn's problem was that Fleming was not alone.
Across a broad front, Rodeka, Hancock, Jackson ran intelligent angles and, as gaps opened, Blair Duncan, and Darren Overton slid through from midfield, and both Tim Horner and Jeremy Wild alternated with long-range booming passes.
To Roslyn's credit, the team never gave in, and reaped some token reward when Dalman and Peter Rae both beat keeper James Waggett late in the match and scored twice to ruined his clean sheet.
Fleming praised his side's general mobility and passing, but singled out the clinical finishing as a major factor in its rampant win.
A possible quarterfinal opponent for Caversham emerged in Christchurch, where penalty shootout heroics from goalkeeper Adam Highfield sealed a 4-3 win for Ferrymead Bays over Western.
In the premier league match at Ocean Grove, Aaron Burgess headed Dunedin Technical into a 15th-minute lead over Grants Braes, but Al Laidler's side hit back with a Doni Dejesus equaliser five minutes later.
A fine display by Braes captain Marcus Mineba, who played in goal due to an injury to regular keeper Josh Columbus, kept Technical at bay until the break.
It took until the 76th minute before Mike Flaws beat Mineba with a far-post header, then Flaws clinched the result with another late goal for the 3-1 result.
At the Caledonian Ground, Northern presented University with an own goal after 24 minutes, and the students went on to earn three points with a 3-1 win.
At Memorial Park, Mosgiel and Spirit FC drew 0-0.
