Cardiff Blues produced an amazing second-half turnaround to see off the challenge of Leeds at the Arms Park.
HEINEKEN CUP POOL TWO
Blues: (6) 40:
Tries: Sowden-Taylor, G Williams 2, Yapp.
Cons: N Robinson 4.
Pens: N Robinson 4.
Leeds: (13) 13:
The Tykes led 13-6 at half-time, but the Blues pack blitzed their opponents with a four-try show after the break.
Hooker Gareth Williams went over twice, Robin Sowden-Taylor and John Yapp both scored, while fly-half Nick Robinson kicked superbly to claim 20 points.
Wing Andre Snyman claimed Leeds' early try, but the English side failed to score a point in the second period.
Thanks to their bonus point the Blues now sit top of Pool Two, after group favourites Perpignan only managed three tries in their 25-6 win out in Italy against Calvisano.
Leeds bullied the Blues pack in a first period that was strangely subdued given the occasion.
To the fore was Leeds' Welsh exile Richard Parks, proving a point in the battle of the openside flankers against Lions tourist Martyn Williams, both of them Pontypridd products.
But the Blues emerged transformed for the second half, with the pack providing the platform - and four tries - for an ultimately impressive win.
After Blues fly-half Robinson's early penalty, Leeds took a firm grip as their forwards made in-roads and sucked in the Welsh defenders.
That allowed former All Blacks scrum-half Justin Marshall the space to nip through an undefended ruck and send Snyman under the posts.
Gordon Ross converted the easy extras, while Marshall added a drop-goal to stretch the English side's lead to 10-3.
Blues fly-half Robinson and Ross exchanged penalties before the break, while Robinson drew first blood after the restart with his third penalty of the afternoon.
That signalled a Blues onslaught as the pack finally took the game to their visitors.
Flanker Sowden-Taylor made the most of an overlap to squeeze in at the left corner, with Robinson adding the first of three superb touchline conversions.
The fly-half's second kick followed another try in that left corner, when Craig Quinnell batted the ball back to Gareth Williams from a lineout and the Blues hooker romped away to score.
The fans in the left corner were then treated to a third Blues try in front of them.
Craig Morgan charged down a kick from Roland de Marigny, who had only just replaced Ross, and prop Yapp had a simple task to score.
Leeds were shell-shocked and it was no surprise that Blues turned the screw.
They claimed an important fourth try and bonus point from a rolling maul that gave hooker Williams his second score, with Robinson adding the conversion and another penalty.
Cardiff Blues coach Dai Young:
"We handed the momentum to Leeds in the first half after a good first 10 minutes, and we had no momentum.
"We had to be much more physical and win the contact area, and we know that if we give a start like that to Perpignan next Friday then it will be very hard to turn things around.
"You have got to win your home games in this competition and at half-time we were under pressure, but in the second period we were much more committed to the tackle area and showed what we could do."
Leeds Tykes coach Phil Davies:
"It was disappointing we capitulated in the way we did. You have got to get results, that is what this business is all about, and it is pretty frustrating at the moment.
"But we are getting there and the first half today was evidence of that. We have got a good set of players, and we have got to start producing performances.
"Everyone is disappointed and frustrated, but the answer to it is hard work. There is no magic wand to be waved, and if you keep working, the law of averages means you will win a game."
Blues: R Williams; Czekaj, J Robinson, Stcherbina, Morgan; N Robinson, Phillips; Yapp, G Williams, M Jones; Quinnell, Sidoli; Sowden-Taylor, M Williams, A Powell. Replacements: T. Davies for Stcherbina (80), R. Powell for Phillips (75), Evans for G. Williams (80), D. Jones for Sidoli (74), Schubert for Sowden-Taylor (76). Not Used: R. Thomas, L. Thomas.
Leeds: Stimpson; Snyman, Vickerman, Jones, Biggs; Ross, Marshall (capt); Kerr, Rawlinson, Gerber; Morgan, Palmer; Thomas, Parks, Crane. Replacements: De Marigny for Ross (68), Care for Marshall (76), Isaacson for Gerber (55), Hyde for Thomas (64). Not Used: Bulloch, Murphy, Doherty.
Referee: Rob Dickson (Scotland).