Hook's 76th-minute penalty preserved the Welsh side's unbeaten home record this season and ensured the title will go right down to the wire.

Tries from Shane Horgan and Felipe Contepomi looked to have done enough to give Leinster a smash-and-grab win against their dominant Welsh hosts.

But Wales international Hook had the last say when he kept his nerve to help the Ospreys turn around a 10-17 deficit to snatch victory at the Liberty Stadium.

Shaun Connor and Contepomi swapped early penalties before the Ospreys made the most of their dominance when scrum-half Justin Marshall raced through under the sticks for a converted score.

But after the Ospreys squandered a host of opportunities Leinster hit them against the run of play when Horgan intercepted Marshall's long pass to race clear and challenge under the posts to make it 10-10 at the interval.

Argentine star Contepomi gave the visitors the lead for the first time moments into the second half when he jinked his way over after Rob Kearney and Chris Whitaker had combined, with Contepomi adding the extras.

The Ospreys sent on Hook and he made an immediate impression with two penalties.

And when Leinster's Jamie Heaslip was sin-binned in the final quarter, Hook and the Ospreys made the most of the numerical advantage to clinch the win.