Swansea stayed on course for a domestic trophy double by dumping arch-rivals Cardiff out of the Principality Cup at St Helen's.

The Welsh-Scottish League leaders booked their semi-final place at the Millennium Stadium next month through three tries during a 20-minute spell from Rhodri Jones, Shaun Payne and Matthew Robinson.

But Swansea still had to withstand a late Cardiff rally after their No 8, Emyr Lewis, crashed over six minutes from time.

Cardiff wing Craig Morgan grabbed a sparkling solo touchdown just before the break, but they lost early momentum when scrum-half Rob Howley was sin-binned for raking his Wales team-mate, Swansea skipper Scott Gibbs.

While Swansea march on, Cardiff's last hope of silverware this season evaporated, leaving coach Lynn Howells facing an uncertain future.

Howells is out of contract at the end of this season and Cardiff could now look for a high-profile replacement. Former England and Lions coach Dick Best has already been linked with the post.

Swansea led by 14 points midway through the second period, but lacked an ability to kill Cardiff off, and Lewis' touchdown guaranteed a nervous finale.

One step ahead

Territorially though, Swansea were comfortably the better side, inspired by outstanding performances from their Wales forwards Colin Charvis, Andy Moore and Darren Morris.

Cardiff led 6-0 inside the opening 10 minutes thanks to two penalties from their Wales fly-half Neil Jenkins.

But when Howley was yellow-carded by referee Paul Adams on advice from his touch judge, Swansea began to enjoy control.

Scrum-half Jones powered over 11 minutes before the break and then a defence-splitting pass by Wales centre Mark Taylor enabled Payne to storm over from 40 metres.

Although Morgan claimed a superb 50-metre kick-and-chase effort, the boot of Swansea fly-half Cerith Rees kept his side 15-11 ahead at the break.

Rees finished with 13 points from three penalties and two conversions and however hard Cardiff tried to keep their season alive, Swansea were always one step ahead.

They now go into the 14 April semi-finals together with Newport and Ebbw Vale, plus the winners of Sunday's quarter-final clash between Bridgend and Neath.

Swansea: Tries: Payne, M. Robinson, R. Jones. Cons: C. Rees 2. Pens: C. Rees 3.

Cardiff: Tries: C. Morgan, E. Lewis. Con: Jenkins. Pens: Jenkins 3.

Teams -

Swansea: K Morgan, S Payne, M Taylor, S Gibbs, M Robinson, C Rees, R Jones, D Morris, G Jenkins, B Evans, T Maullin, A Moore, P Moriarty, C Charvis, G Lewis.
Replacements: S Martens, G Henson, D Smith, C Anthony, Griffiths, L Jones, D Thomas.

Cardiff: R Williams, N Walne, J Robinson, G Thomas, C Morgan, N Jenkins, R Howley, S John, J Humphreys, D Young, C Quinnell, M Voyle, D Baugh, M Williams, E Lewis.
Replacements: R Powell, M Rayer, G Kacala, W Fyvie, S Moore, K Fourie.

Att: 7000

Referee: Paul Adams (Welsh RFU)