Hook landed all his penalty attempts at goal against Leinster
Ospreys: (10) 19
Pens: Connor, Hook (3)
Leinster: (10) 17
James Hook came off the bench to keep the Ospreys in the Magners League title hunt by kicking his side to victory over leaders Leinster in Swansea.
Tries: Horgan, Contepomi
Con: Contepomi (2)
The rising star hit three second-half penalties to secure a comeback win.
Shaun Connor's penalty and a Justin Marshall try opened a 10-3 lead for the Ospreys, but Shane Horgan's try levelled matters just before the break.
Felipe Contepomi converted his own superb solo try to put Leinster ahead, but Hook came to the Ospreys' rescue.
The victory takes the Ospreys up to second above Ulster and to within two points of Leinster with a game in hand.
Despite the importance of the game to the home side's title aspirations, the Ospreys decided to rest star-man Hook, so Connor started at fly-half.
He wasted the only scoring opportunity of the opening quarter when he hooked a simple penalty wide of the posts.
Another penalty in front of the posts after 25 minutes saw Connor atone for the earlier miss, but Contepomi levelled the scores moments later with a classy long-range effort.
Connor then played a significant role in Marshall's try when he found some space down the blindside before finding Filo Tiatia.
The number eight's attempted pass went astray, but the ball fell perfectly for Marshall to burst over the line.
Connor converted, and was then denied a try when Gordon D'Arcy's superb tackle forced into touch in the left corner.
But Leinster drew level moments before the break when Marshall turned from hero to villain.
His woeful pass under no pressure was easily intercepted in midfield by Horgan and the centre had enough pace to beat the cover defence.
Contepomi's conversion brought Leinster level in a half they hardly threatened the home defence.
Leinster added some much-needed intensity to proceedings after the break and their attacking intension was rewarded with Contepomi's magical solo try on 47 minutes.
The fly-half burst down the left flank after receiving the ball on the halfway line, and showed pace, balance and strength to beat three Ospreys defenders to score.
The conversion was a formality, and the seven-point deficit prompted Ospreys coach Lyn Jones to bring Hook to the field in place of Connor.
The replacement needed less than 10 minutes to make an impact as his 40-metre penalty cut Leinster's lead to five points.
Another Hook penalty brought the home side to within a point as the game, and the young fly-half completed the comeback six minutes before time with another composed kick.
Ospreys: Terblanche; Walker, Parker, A. Bishop, S. Williams; Connor, Marshall; James (capt), Bennett, A. Jones, A.W. Jones, Thomas, R. Jones, Pugh, Tiatia.
Replacements: Byrne for Terblanche (60), Hook for Connor (50), D. Jones for James (54), Hibbard for Bennett (60).
Not Used: Powell, Beech, Roberts.
Leinster: Dempsey; Kearney, D'Arcy, Horgan, Fitzgerald; Contepomi (capt), Whitaker; Corrigan, Blaney, Green, Hogan, O'Kelly, Keogh, Gleeson, Heaslip.
Replacements: Lewis for Fitzgerald (65), Jowitt for Corrigan (76), Jackman for Blaney (40), Wright for Green (40).
Not Used: Finegan, Easterby, Warner.
Ref: Peter Allan (SRFU).