The rising star of Welsh rugby soon made his presence felt and his three pin-point penalties enabled the home side to overtake Leinster and steal a win that puts the title a step closer to returning to Wales.
The Leinster defence was magnificent all night and there was no score from either side in the opening quarter. Then a Connor penalty and try from Justin Marshall pushed the Ospreys into a 10-3 lead.
Shane Horgan's try, and Felipe Contepomi's conversion, levelled matters just before the break and Leinster skipper Contepomi skipped away for a brilliant solo try to give his side a 17-10 lead.
The 10,000+ crowd were fearing the worst but Hook's introduction gave them new hope. As the pressure from the home side mounted, so Hook rewarded his team with three penalties.
The last one came six minutes from time and moved the Ospreys up into second place in the table to within two points of Leinster at the top. The Ospreys also have a game in hand over the Irish side.
Ospreys: Try: J Marshall. Con: S Connor. Pens: J Hook (3), S Connor
Leinster: Tries: S Horgan, F Contepomi. Cons: F Contepomi (2). Pen: F Contepomi
Ospreys: S Terblanche (L Byrne 60); N Walker, S Parker, A Bishop, S Williams; S Connor (J Hook 50), J Marshall; P James (D Jones 54, capt), H Bennett (R Hibbard 60), A Jones, AW Jones, J Thomas, R Jones, R Pugh, F Tiatia
Leinster: G Dempsey; R Kearney, G D'Arcy, S Horgan, L Fitzgerald (K Lewis 65); F Contepomi (capt), C Whitaker; R Corrigan (C Jowitt 76), B Blaney (B Jackman 40), W Green (S Wright 40), T Hogan, M O'Kelly, S Keogh, K Gleeson, J Heaslip
Referee: Peter Allan (SRFU)