The Ospreys, fielding a string of youngsters in their team, set the seal on their LV= Cup campaign with a 21-17 win over Leeds on Thursday.
The Welsh side seemed to be cruising to victory after tries from Hanno Dirksen, Steve Tandy and Jamie Nutbrown helped them open up a 21-10 lead.
But a late rally saw Leeds earn a converted penalty try in injury time and make it a nervous few minutes for the home side, who had lost all their previous three games against Northampton, Bath and Gwent Dragons.
The Ospreys gave debuts to 18-year-old South African-born Dirksen and Aberavon hooker Marc Breeze. Tom Prydie, 17, was again released by the Wales squad to take his place at full-back.
The Ospreys just about deserved their 14-10 interval lead with tries from Dirksen and Tandy.
Leeds opened the scoring after 11 minutes with a penalty goal for Joe Ford and made it difficult for the Ospreys to get any quick recycled ball at the breakdown.
To spark the Ospreys into try-scoring action it took a fine floated pass from outside-half Gareth Owen out to Dirksen, who showed strength and speed to beat the first man and pass out of the tackle to Ashley Beck.
And it was centre Beck who helped the wing over into the corner. Prydie converted from the touchline to put the home side into a 7-3 lead after 20 minutes.
Dirksen was nearly over again soon after. He collected a neatly struck Owen cross kick only to go into touch five metres short.
A second Ospreys try came after Prydie had watched a 40-metre penalty attempt rebound off a post. More good work from Dirksen and the lively Nutbrown, saw Owen put a grubber in for Steve Tandy - on his 101st appearance - to slide in.
For the rest of the half the Ospreys were forced to show their defensive skills and they did very well to prevent a Leeds try until the final minute of normal time, scored by lock Erik Lund.
The Ospreys enjoyed the better of the exchanges early in the second half but could not turn pressure into points - Prydie missing two penalty shots in the space of three minutes.
But the pressure finally told when Nutbrown dashed from a scrum on the 22 and squeezed over by the posts for the Ospreys third converted try.
If the Ospreys thought they were cruising to victory they were made to think again when prop Ryan Bevington was sin-binned for a professional foul.
At the end Leeds were awarded a penalty try but it was not enough.
For the Ospreys:
Tries: Tandy, Nutbrown, Dirksen
Cons: Prydie 3
Tries: Lund, penalty try
Cons: Ford 2
Ospreys: 15 Tom Prydie, 14 Hanno Dirksen, 13 Sonny Parker, 12 Ashley Beck, 11 Jonny Vaughton, 10 Gareth Owen, 9 Jamie Nutbrown, 8 Tom Smith, 7 Steve Tandy, 6 Jerry Collins (c), 5 Ian Evans, 4 Andy Lloyd, 3 Craig Mitchell, 2 Marc Breeze, 1 Ryan Bevington.
Replacements: 16 Ed Shervington, 17 Cai Griffiths, 18 Will Taylor, 19 Richard Kelly, 20 Conor McInerney, 21 Ben Lewis, 22 Rhys Webb, 23 Ben John.
Leeds: 15 Leigh Hinton, 14 Peter Wackett, 13 Henry Fa'afili, 12 Scott Barrow, 11 Lee Blackett, 10 Joe Ford, 9 Joe Bedford, 8 Rhys Oakley, 7 Calum Clark, 6 Jon Pendlebury, 5 Marco Wentzel (c), 4 Erik Lund, 3 Peter Bucknall, 2 Andy Titterrell, 1 Gareth Hardy.
Replacements: 16 Vili Ma'asi, 17 Mike MacDonald, 18 Juan Gomez, 19 Phil Murphy, 20 Kearnan Myall, 21 Andy Gomarsall, 22 Ceiron Thomas, 23 Richard Welding.
Referee: Gwyn Morris (Wales)