The Scottish side withstood pressure from the Welsh visitors until Ben Blair’s penalty after 19 minutes. But James went over for a try, converted by Blair, and fellow winger Jamie Roberts went over the line a second time before the break.
Second-half home pressure failed to produce points and James added a try and ended Edinburgh’s outside hopes of becoming the first Scottish team to win the league title.
The opening quarter had been a war of attrition with the sides sounding each other out. Cardiff Blues broke the deadlock with a pinpoint penalty by Blair and two tries in the space of seven minutes swung the contest decisively in favour of the Blues.
First, James was in the right place at the right time to finish clinically in the wake of a series of patient phases, with skipper Xavier Rush in the thick of things. Then Roberts struck following a defensive disaster on the part of the hosts.
Roberts appeared to be marshalled by Hugo Southwell and Ben Cairns when he received the ball close to the touchline. But Southwell’s initial challenge was brushed off with contempt and Cairns’s attempt to reel in the winger from behind never looked like succeeding.
Edinburgh looked more purposeful after the restart, but they were up against a superbly-drilled Arms Park outfit. Simon Webster had a great chance to narrow the gap, but he was felled by a crunching tackle from Tom Shanklin. John Houston was then blocked inches short of the line following a quickly-taken tap penalty by Mike Blair.
Having weathered the early second-half storm, Cardiff began to reassert their superiority and Roberts went close to notching his double. They kept up the momentum and effectively sealed the fate of the Gunners with another excellent touchdown from James.
Again the build-up was composed and secure before the time and space was created for James to scorch through, taking advantage of the committed markers.
Edinburgh: Southwell, Webster, Cairns, De Luca, Houston, Godman, M. Blair, Kerr, Kelly, Smith, Mustchin, Hamilton, S. Cross, Hogg, Callam.
Replacements: MacRae for De Luca (69), Turnbull for Houston (57), Meyer for M. Blair (72), Allori for Kerr (59), Gissing for Hamilton (44), Pringle for S. Cross (71). Not Used: Lawrie.
Blues: Blair, J. Roberts, Shanklin, G. Thomas, James, Flanagan, Spice, Jenkins, G. Williams, Filise, D. Jones, Tito, Molitika, M. Williams, Rush.
Replacements: Stcherbina for Shanklin (68), N. Robinson for Flanagan (62), Rees for Spice (75), Yapp for Jenkins (68), R. Thomas for G. Williams (25), Morgan for Tito (54), White for M. Williams (65).
