Saracens retained their position at the top of Pool 5 after claiming the spoils in an entertaining clash at Wembley Stadium, winning 31-26 on Saturday.
After a tight contest throughout, Sarries managed to hold on to claim victory, leaving them in pole position to make the competition knockouts.
They got off to the best of starts, as went over for a try after just three minutes. Great work through the phases after a stolen Ospreys line-out allowed Rhys Gill in to score. Owen Farrell added the conversion, a dream opening for the Saracens.
Ospreys reduced the deficit soon after from a Dan Biggar penalty, only for Farrell to strike back.
The Ospreys were slow to get into their stride, but levelled the scores soon after, when a lucky bounce allowed impressive inside centre Ashley Beck in for a try, Biggar adding the extras.
In an end to end opening quarter, Saracens responded almost immediately with a try of their own, number eight Ernst Joubert grounding the ball after fine scrummaging from the Sarries.
As was with the theme of the first half though, Ospreys stayed in touch from another Biggar penalty, the game now shaping up to be a pulsating contest.
Saracens were perhaps looking the better side in the first half, and stretched their lead again before the break, Farrell adding another two penalties either side of a sin-binning for Ospreys' captain Tom Smith, to leave ten between them at the break.
The Welsh side started well after the restart with a Dan Biggar penalty, but Saracens didn't take long to restore a fairly sizeable lead, when Chris Wyles dived over for their third try after great work from Schalk Brits.
The Ospreys were looking the hungrier team in the second half though, and came within five points when Beck crossed for his second try, Biggar converting.
However, they just couldn't peg back the Saracens as both sides traded penalties late on, the Saracens eventually claiming victory by five points. Their rematch is next Friday.
Tries: Gill, Joubert, Wyles
Con: Farrell 2
Pen: Farrell 4
Tries: Beck 2
Con: Biggar 2
Pen: Biggar 4
Saracens: 15 Alex Goode, 14 David Strettle, 13 Owen Farrell, 12 Brad Barritt, 11 Chris Wyles, 10 Charlie Hodgson, 9 Ben Spencer, 8 Ernst Joubert, 7 Jacques Burger, 6 Kelly Brown, 5 Mouritz Botha, 4 Steve Borthwick, 3 Matt Stevens, 2 Schalk Brits, 1 Rhys Gill.
Replacements: 16 Jamie George, 17 Deon Carstens, 18 Carlos Nieto, 19 George Kruis, 20 Andy Saull, 21 Peter Stringer, 22 Adam Powell, 23 James Short.
Ospreys: 15 Richard Fussell, 14 Tommy Bowe, 13 Andrew Bishop, 12 Ashley Beck, 11 Shane Williams, 10 Dan Biggar, 9 Rhys Webb, 8 Joe Bearman, 7 Justin Tipuric, 6 Tom Smith, 5 Jonathan Thomas, 4 Ryan Jones, 3 Adam Jones, 2 Richard Hibbard, 1 Duncan Jones.
Replacements: 16 Huw Bennett, 17 Ryan Bevington, 18 Aaron Jarvis, 19 Ian Gough, 20 George Stowers, 21 Tom Isaacs, 22 Matthew Morgan, 23 Sonny Parker.
Referee: Pascal Gauzere (France)