Dan Biggar's haul of 20 points kept the Ospreys' season alive as they edged past Pro12 leaders Leinster with a 25-19 victory.
The Welsh region are now level on points with Glasgow, who occupy the fourth and final play-off position, having played two games more.
Two Biggar penalties to one from Leinster's Jimmy Gopperth saw Ospreys take a 6-3 lead going into the second quarter of the match.
Biggar then missed with a snap drop goal attempt and Hassler was stopped just short of the line after a desperate last-ditch tackle by Shane Jennings.
However Ospreys stretched their lead by seven when Richard Fussell's sublime flick on under intense pressure found Jeff Hassler who crossed wide out on the right for a try which Biggar improved from the touchline.
Ospreys failed to deal with the restart though and Leinster hit straight back from an attacking lineout, with Ireland prop Cian Healy dotting down at the back of a driving maul.
Gopperth's conversion saw the sides separated by three points at the break. Neither side managed any further tries after the interval - not that the half was without incident or chances.
Biggar butchered a golden opportunity to wrap the game up well before the final whistle when he failed to gather in a pass after lock Alun Wyn-Jones had opened up the Leinster defence with a surging run down centre field.
Unmarked Leinster wing Dave Kearney was guilty too of spilling a well-weighted cut out pass from Gopperth when it seemed inevitable he would score.
Two Biggar penalties to three from Gopperth saw the scores tied at 19-19 and a second draw of the season between the sides looked on the cards until the Ospreys fly-half intervened with a drop goal and a late penalty.
Pens: Biggar 5
Drop Goal: Biggar
Pens: Gopperth 4
Ospreys: 15 Richard Fussell, 14 Jeff Hassler, 13 Jonathan Spratt, 12 Ashley Beck, 11 Aisea Natoga, 10 Dan Biggar, 9 Tom Habberfield, 8 Dan Baker, 7 Justin Tipuric, 6 Joe Bearman, 5 Alun-Wyn Jones (c), 4 Ryan Jones, 3 Aaron Jarvis, 2 Scott Baldwin, 1 Duncan Jones.
Replacements: 16 Scott Otten, 17 Nicky Smith, 18 Adam Jones, 19 James King, 20 Morgan Allen, 21 Tito Tebaldi, 22 Sam Davies, 23 Hanno Dirksen.
Leinster: 15 Rob Kearney, 14 Zane Kirchner, 13 Gordon D'Arcy, 12 Noel Reid, 11 Dave Kearney, 10 Jimmy Gopperth, 9 Isaac Boss, 8 Jamie Heaslip , 7 Shane Jennings, 6 Kevin McLaughlin, 5 Mike McCarthy, 4 Leo Cullen (c), 3 Martin Moore, 2 Sean Cronin, 1 Cian Healy.
Replacements: 16 Aaron Dundon, 17 Michael Bent, 18 Mike Ross, 19 Devin Toner, 20 Jordi Murphy, 21 Luke McGrath, 22 Collie O'Shea, 23 Darragh Fanning.
Referee: Marius Mitrea (Italy)
Assistant Referees: Ian Davies (Wales), Jon Mason (Wales)