Warriors produced another late, late show to book their place in the European Challenge Cup quarter-finals for the first time in a decade.
Acting captain Ryan Mills slotted a superb drop goal from 30 metres with under 10 seconds left on the clock to secure another memorable victory. Although Mills struck the kick well it took a deflection from an Ospreys player before it squeezed between the posts.
Tries from Jonny Arr, Ollie Lawrence and Dean Hammond helped Warriors to become only the second team to beat Ospreys at home this season but this was also a triumph for the Warriors coaching team.
Head Coach Rory Duncan said before the match that Warriors had rehearsed countering Ospreys long kicking game and so it proved.
Warriors dropped mills, Scott van Breda and Arr back in defence to frustrate Ospreys and they out-manoeuvred the Welsh side at their own tactics to snatch a deserved win.
Warriors have already secured top spot in Pool Two but need to a bonus point win against Stade Francais at Sixways on January 19 to ensure they will be at home in the quarter-finals at the end of March.
Warriors topped and tailed the scoring which they started in the 11th minute when Darren Barry intercepted on half way and raced 40 metres before Jonny Arr arrived in support and raced away to dot down for the try which Scott van Breda converted fromwide on the left.
But Ospreys soon got their revenge with an interception try of their own. It looked like Warriors would score themselves when Wales wing George North lost the ball in contact.
But Ospreys left wing Keelan Giles then snaffled a pass from Ollie Lawrence and he went almost the length of the pitch to score despite the efforts of van Breda to haul him in.
Luke Price was off target with his conversion kick but the fly-half made no mistake with a more straightforward penalty after 24 minutes which nudged Ospreys ahead.
Warriors produced some patient rugby in attack but their hard work was undone when another stray pass gave Ospreys the opportunity to turn defence into attack. Sustained pressure led to flanker Olly Cracknell crossing just before the break with Price adding the extras.
Warriors trimmed the deficit when Lawrence again demonstrated his class by powering away for an unconverted try and they regained the lead midway through the second half when a sustained attack wore down Ospreys and Hammond went over.
Lawrence almost went over again when he intercepted close to the line but he was hauled down by George North and left the field suffering from cramp.
Ospreys eventually kept possession for a few phases and built pressure from which Sam Davies kicked a penalty which looked like being the winner.
But Warriors again dug deep in adversity and Mills capped a fine performance with a perfectly timed drop goal which sealed another breathless win.
Warriors | 15 Scott van Breda, 14 Tom Howe, 13 Ollie Lawrence (Butler 55), 12 Ben Te’o, 11 Dean Hammond, 10 Ryan Mills (C), 9 Jonny Arr (Heaney 79), 1 Ethan Waller, 2 Joe Taufete’e (Annett 66), 3 Simon Kerrod, 4 Darren Barry (Kitchener 63), 5 Pierce Phillips, 6 Ted Hill, 7 Marco Mama (Kirwan 50), 8 Matt Cox.
Replacements | 16 Niall Annett, 17 Jack Cosgrove, 18 Joe Morris, 19 Andrew Kitchener, 20 Carl Kirwan, 21 Michael Heaney, 22 Will Butler, 23 Nick David.
11m | Arr try 0-5
12m | van Breda con 0-7
18m | Giles try 5-7
24m | Price pen 8-7
34m | Cracknell try 13-7
35m | Price con 15-7
49m | Lawrence try 15-12
57m | Hammond try 15-17
75m | Davies pen 18-17
80m | Mills drop goal 18-20