The defending champion Ospreys hav booked their place in this season's EDF Energy Cup semi-finals, with an all important losing bonus point, having lost to London Irish 23-19 away at the Madejski Stadium on Sunday.

London Irish side led 20-6 just after half-time. But with fly-half James Hook's precision goalkicking - he booted 14 points - and winger Nikki Walker's 54th minute touchdown kept Ospreys in contention.

Irish dominated territory and possession for large parts of a stirring Madejski Stadium encounter, yet victory was still not enough to end Ospreys' reign as Anglo-Welsh cup kings.

London Irish full-back Peter Hewat kicked 13 points, but despite Ospreys hanging on for dear life during the closing seconds, Irish could not administer a telling blow.

Irish, fully aware they still had a semi-final chance, paraded 11 internationals and had no intention of playing second fiddle to the cup holders.

Hook booted the Ospreys into a 6-0 lead inside 20 minutes, but Irish had already built an imposing territorial platform - and they prospered with devastating effect.

London Irish finally broke through Ospreys defence nine minutes before half-time.

Aggressive approach work by the Irish pack, with flanker Steffon Armitage and skipper Bob Casey in the driving seat, eventually took its toll.

And Mapusua was the recipient of Shane Geraghty's pass, crashing over near the posts for a try that Hewat converted.

We then saw a second try from Tagicakibau as he set off on an unopposed 50-metre sprint.

Hewat added the extras, following an earlier penalty, hoisting Irish 17-6 clear as Ospreys full-back Jonny Vaughton departed injured on the stroke of half-time and was replaced by Andrew Bishop.

Hewat and Hook exchanged penalties early in the second period, and although the Ospreys had no reason to panic, coach Sean Holley made a double 52nd-minute substitution.

Forwards Ryan Jones and Alun-Wyn Jones, who will both start for Wales against world champions South Africa next Saturday, entered the fray, and there was an immediate urgency about Ospreys' play.

Barely 100 seconds after the reinforcements arrived, Ospreys struck, as Bishop's weaving run caused panic in the Irish defence and Walker finished off a crisp move.

Hook converted, cutting Ospreys' deficit to just four points, but there was also an injury scare for the visitors - and Wales coach Warren Gatland - as hooker Huw Bennett limped off.

The Ospreys had an impressive comeback, but there was yet another Hewat penalty - his third - made it 23-16 entering the closing quarter, as Irish player/coach Mike Catt replaced Geraghty.

If the Ospreys were not going to win, they knew it was a case of remaining within a losing bonus-point range.

And Hook certainly played his part, booting a magnificent 52-metre penalty that meant Irish's lead was back to four points with little more than 10 minutes left.

Marty Holah did go over, which would have put the Ospreys in front, but his tray was controversially ruled out for a forward pass.

The finale proved an inevitably tense business, with errors creeping in on both sides, but the Ospreys held on to book a semi-final place at Coventry's Ricoh Arena next March.

The scorers:

For London Irish:
Tries: Mapusua, Tagicakibau
Cons: Hewat 2
Pens: Hewat 3

For Ospreys:
Tries: Walker
Cons: Hook
Pens: Hook 4

London Irish: 15 Peter Hewat, 14 Topsy Ojo, 13 Elvis Seveali'i, 12 Seilala Mapusua, 11 Sailosi Tagicakibau, 10 Shane Geraghty, 9 Paul Hodgson, 8 Chris Hala'Ufia, 7 Steffon Armitage, 6 Richard Thorpe, 5 Bob Casey, 4 James Hudson, 3 Faan Rautenbach, 2 David Paice, 1 Clarke Dermody.
Replacements: 16 Tonga Lea'aetoa, 17 James Buckland, 18 Kieran Roche, 19 Declan Danaher, 20 James Bailey, 21 Peter Richards, 22 Mike Catt.

Ospreys: 15 Jonny Vaughton, 14 Nikki Walker, 13 Tommy Bowe, 12 Gavin Henson, 11 Shane Williams, 10 James Hook, 9 Jamie Nutbrown, 8 Filo Tiatia, 7 Marty Holah, 6 Tom Smith, 5 Ian Evans, 4 Ian Gough, 3 Adam Jones, 2 Huw Bennett, 1 Paul James (c).
Replacements: 16 Richard Hibbard, 17 Craig Mitchell, 18 Lyndon Bateman, 19 Ryan Jones, 20 Rhys Webb, 21 Dan Biggar, 22 Andrew Bishop.

Referee: Andrew Small (England)
Touch judges: Andrew Pearce (England), Roger Baileff (England)
Assessor: Ed Morrison (England)
Television match official: John Burtenshaw (England)