Ben White goes over for one of Cardiff Blues' five tries
Blues 36 (10)
Tries: Shellard 2, Rush, White, J Robinson.
Cons: Blair 4.
Borders 15 (8)
Tries: Danielli, Law.
Cardiff Blues kept their 100% Magners League home record with a five-try win over bottom side Border Reivers.
But it took a purple patch just after half-time to break the Scots who had stayed in touch through Welsh mistakes.
Rhys Shellard's opener for Blues was cancelled out when Simon Danielli intercepted a loose Nick Robinson pass.
But Xavier Rush, Ben White, Jamie Robinson, and Shellard again all struck in the second half, with Borders getting a consolation from Gary Law.
It all looked so simple when the home side crafted a superb try inside two minutes.
In-form Blues scrum-half Mike Phillips began the move with a brilliant long pass, after a misdirected Gregor Townsend kick rebounded off the back of one of his own forwards.
Ben Blair was involved twice, with sterling support from flanker-turned-lock Scott Morgan, before Shellard stretched out of a tackle to place the ball on the line and Blair converted.
But wrong options and handling errors wasted home possession, allowing the Reivers to claim a penalty by skipper Calum MacRae and then go ahead with a bizarre score.
As with the opener, it came from a misplaced Townsend kick, retrieved by opposite number Nicky Robinson.
Deep in his own 22, the Blues fly-half hurled the ball blindly behind him, but instead of a team-mate it found Border wing Danielli, who touched down gratefully.
The Blues regained the lead with a Blair penalty after a late tackle by prop Gavin Kerr which saw the Scot sin-binned, and they should have had three more points but for an amazing blunder by Irish referee Peter Fitzgibbon.
With advantage to the Blues, fly-half Robinson slotted a drop-goal straight between the posts, only for the official, presumably believing it had missed, to take play back for an unproductive penalty.
It was just after the Scots had returned to full strength that the Blues finally claimed their second try, captain Rush blasting through beneath the posts. Blair again converted.
The Welshmen might have been awarded a penalty try when Danielli illegally pulled Chris Czekaj back, but it mattered little as Aussie flanker White crossed moments later.
And a third try in seven minutes, made by Nicky Robinson for brother Jamie, with a contribution from Czekaj, clinched the bonus point.
Amid a flurry of comings and goings, the Borders grabbed a consolation try when replacement wing Law won a kick and chase for MacRae to add the extras.
But the game ended as it began, with Shellard once again racing over and Blair's emphatic kick completing the job.
Blues: Blair; James, J. Robinson, Stcherbina, Czekaj, N. Robinson, Phillips, Jenkins, Thomas, G. Powell, Jones, Morgan, Shellard, White, Rush.
Replacements: Roberts, G. Williams, Down, Powell, Fairhurst, Luveitasau, Macleod.
Reivers: MacRae (capt), Danielli, De Luca, Rennie, Daniel, Townsend, Chrystie, Kerr, Scott, Kalman, Grimes, Palepoi, Gray, Miller, Brown.
Replacements: Ford, Douglas, Newlands, Dalziel, McKerchar, Jones, Law.
Referee: Hugh Watkins (WRU).