The Ospreys claimed an important seven-try 48-17 victory over Ulster at the Liberty Stadium on Friday, thereby boosting their quest for a Heineken Cup quarter-final place.
The teams meet again in Belfast next Friday night, when Ospreys coach Lyn Jones will demand a repeat performance after seeing his side post their biggest Heineken Cup win.
But Ulster's European campaign is all over bar the shouting, leaving them lurching towards a pool stage exit for the ninth successive season.
The Ospreys desperately needed victory after coming unstuck at Gloucester last time out, and they went into battle as red-hot favourites, parading a team of 15 internationals.
Hook took the fly-half role Henson filled against Quins, while Ulster were without injured number eight Roger Wilson, which meant lock Matt McCullough switching to back-row duties.
Ospreys blasted out of the blocks, taking a fifth-minute lead when full-back Lee Byrne's beautifully-timed run enabled him to send Parker over wide out.
And they should have scored again just three minutes later, but wing Shane Williams' brilliant 50-metre break did not gain the reward it deserved after he was tackled and his unmarked support runners got their angles wrong.
Ospreys though, bagged a second try inside the opening quarter following sustained pressure that saw Ulster inevitably run out of defensive numbers and Marshall crossed unopposed.
Fly-half Paddy Wallace reduced Ulster's deficit by slotting an angled penalty, and the Ospreys could make no further inroads before the break.
The second period was all about Ospreys going in pursuit of a bonus point, but once it arrived they didn't take their foot off the pedal.
Only some committed tackling kept out a hungry back division, although Ulster were powerless to stop Walker and Byrne completing a six-try Ospreys performance.
The victory surpassed their previous biggest Heineken Cup win of 46-19 against Harlequins in 2004, and flashed a warning signal to Gloucester - impressive bonus-point victors over Bourgoin in France on Friday - that the group outcome is not a foregone conclusion. The scorers: For Ospreys:
Tries: Parker, Marshall, AW Jones, Tiatia, Walker 2, Byrne
Cons: Hook 5
Pens: Hook For Ulster:
Tries: Boss, Danielli
Cons: Wallace 2
Pens: Wallace Ospreys:
15 Lee Byrne, 14 Nikki Walker, 13 Mark Taylor, 12 Sonny Parker, 11 Shane Williams, 10 James Hook, 9 Justin Marshall, 8 Filo Tiatia (c), 7 Marty Holah, 6 Jonathan Thomas, 5 Ian Evans, 4 Alun Wyn Jones, 3 Adam Jones, 2 Huw Bennett, 1 Duncan Jones Replacements:
16 Richard Hibbard, 17 Cai Griffiths, 18 Ian Gough, 19 Ben Lewis, 20 Mike Phillips, 21 Shaun Connor, 22 Andrew Bishop Ulster:
15 Bryn Cunningham, 14 Tommy Bowe, 13 Andrew Trimble, 12 Paul Steinmetz, 11 Simon Danielli, 10 Paddy Wallace, 9 Isaac Boss, 8 Matt McCullough, 7 David Pollock, 6 Neil Best, 5 Carlo Del Fava, 4 Justin Harrison, 3 Bryan Young, 2 Rory Best (c), 1 Justin Fitzpatrick Replacments:
16 Declan Fitzpatrick, 17 Matt Miles, 18 Ryan Caldwell, 19 Kieron Dawson, 20 Kieran Campbell, 21 Niall O'Connor, 22 Rob Dewey Date:
Friday, December 7 Venue:
Liberty Stadium Kick-off:
20:00 GMT Referee:
Chris White (England) Touch judges:
Ashley Rowden (England), Andrew Pearce (England)