Blues (13) 24
Tries: Molitika, Filise Con: Blair Pens: Blair 4
Bath (3) 18
Tries: Penalty try, Higgins Con: Berne Pens: Cuthbert, Maddock
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Highlights: Cardiff Blues 24-18 Bath
Cardiff Blues booked their place in the EDF Energy Cup semi-finals with a hard-fought home win over Bath.
The excellent Maama Molitika scored the Blues' opening try, with Ben Blair kicking them to a 13-3 half-time lead.
Bath were awarded a penalty try after Joe Maddock was prevented from scoring by Jason Spice's high tackle.
Taufa'ao Filise shunted over to restore the Blues' lead and despite a late try by Andrew Higgins, Blair's boot kept Bath at arm's length at the Arms Park.
Bath drew first blood with an early Jack Cuthbert kick, the Blues penalised for dropping a scrum.
But the hosts hit back immediately as Nick Robinson's inside pass tricked the Bath line to send brother Jamie through a hole, the centre treating supporting back-row Molitika with a perfect offload that saw the Tongan lope under the posts.
Blair added the conversion, the full-back following that with two penalties to reward the Blues' territorial advantage in the first quarter.
The New Zealander's second of those penalties brought the full-back's points tally for the season so far to a century.
We gave Bath far too much but we showed a lot of determination to come away with that victory
Cardiff Blues director of rugby Dai Young
The English side slowly earned a foothold in the game and Bath's two wings, Maddock and Higgins, made good breaks that had the Blues defence scrambling back.
Also catching the eye was Shontayne Hape, the rugby league convert, who was giving as good as he got in the midfield exchanges against Tom Shanklin and Jamie Robinson.
But all too often the visitors spilled the ball at the crucial point or conceded possession for lack of support.
Cuthbert had the chance of giving Bath some reward but the full-back pushed his second kick wide of the right-hand post.
Bath laid siege to the Blues line as the half ran out, even opting for a five-metre scrum instead of taking a penalty kick, but the Welsh defence held firm.
The Guinness Premiership side suffered an early blow when Cuthbert was forced off early in the second half, getting his tackling position all wrong and suffering a nasty blow to the head as a result.
Maddock took over Bath's kicking duties and stroked over his first effort after Shanklin was sent to the sin-bin for hands at the ruck once too often.
But the English side immediately conceded a penalty of their own and Blair stepped up to put the Blues two scores clear once more at 16-6.
Then came an amazing passage of play, sparked by a fine turn of pace from Maddock that sent him racing towards the try line.
The wing stepped neatly inside Spice, who stuck out an arm that caught Maddock round the neck and sent him spinning to the turf.
Referee Nigel Owens awarded a penalty try but opted not to sin-bin Spice, ruling the scrum-half's infraction was only accidental.
Even then the drama was not over as Maddock, possibly still slightly dazed, took the conversion from in front of the posts but saw his kick charged down by the on-rushing Richard Mustoe.
Blues still led 16-11 and Blair had the chance to extend the lead once again but his trusty boot at last failed and his penalty sailed wide.
But the hosts used their pack to good advantage and drove to within touching distance of the Bath line and forced a close-range scrum.
Molitika drove from the base and although he was stopped short, prop Filise barged over.
If the Blues thought that had secured the win they were made to think again as Bath put together a cutting move with six minutes remaining.
Swift hands carved space and Higgins cut in from the wing to score, Shaun Berne's conversion cutting Bath's deficit to just 21-18.
But the late sin-binning of Bath replacement Stuart Hooper allowed Blair to strike his fourth penalty and usher the Blues into the semi-finals of the competition.
Cardiff Blues director of rugby Dai Young:
"I think we've played better in the last couple of weeks.
"But in saying that I thought we showed a lot of guts, a lot of determination, we rode our luck on occasions as well but we'll take that.
"We gave them far too much possession, far too much field position but we showed a lot of determination to come away with that victory."
Bath coach Steve Meehan:
"I was disappointed with our first-half display, but I thought we improved after the break.
"We gifted Cardiff a soft try early on and made it difficult for ourselves.
"Some of our guys gave a good account of themselves. Danny Grewcock and Andy Beattie did well in their first games back after injury."
Cardiff Blues: Blair; Mustoe, J. Robinson, Shanklin, James; N. Robinson, Spice; Yapp, G. Williams, Filise, Jones, Tito (capt), Molitika, Sowden Taylor, Lewis.
Replacements: G. Thomas, Sweeney, Rees, G. Powell for Yapp (31), Johnson, Morgan for Tito (63), M. Williams for Lewis (63).
Sin Bin: Shanklin (52).
Bath: Cuthbert; Maddock, Crockett (capt), Hape, Higgins; Berne, Bemand; Flatman, Dixon, Bell, Short, Grewcock, Beattie, Scaysbrook, Browne.
Replacements: Hawkins for Dixon (76), Jarvis for Bell (53), Catt for Flatman (59), Hooper for Grewcock (41), Faamatuainu for Beattie (47), Baxter, Cheeseman for Cuthbert (44).
Sin Bin: Hooper (80).
Referee: Nigel Owens (WRU).