Ice-cool Walker struck a first-half double before Ryan Jones added a third try after the interval to sink their arch rivals in sub-zero temperatures at the Liberty Stadium.
And the convincing result allowed Sean Holley’s men to re-establish a healthy two-point lead over Glasgow Warriors at the summit of the table.
The Blues began brightly but the visitors failed to recover once Dan Biggar scored a deft drop goal on 12 minutes.
Ben Blair and Biggar both missed long distance penalty chances before the Ospreys scored a debatable opening try at the end of a feisty first quarter.
Irish wing Tommy Bowe appeared to be offside chasing Biggar’s chip and full-back Blair was turned over once he gathered the ball in his own 22.
But Welsh referee James Jones signalled for play to continue and quick service from Ricky Januarie and Jonathan Thomas sent Nikki Walker clear in the left corner.
Biggar failed to convert from the left touchline but the Ospreys held a commanding 8-0 lead as the snow began to descend at the Liberty Stadium.
There was a concern for the Blues and Wales with Tom Shanklin limping off with a foot injury in the 33rd minute to be replaced by Gareth Thomas.
But there was little the Wales veteran could do as the Ospreys doubled their try count seconds later.
Biggar cut through a gaping hole left by half-back pair Sam Norton-Knight and Richie Rees and slick handling from Andrew Bishop, Sonny Parker and Lee Byrne handed Walker the chance to scorch over for his second score from close-range.
The Blues responded with a late rally as the opening period drew to a close but Richard Mustoe saw his dash for the try-line denied by a superb covering tackle by Byrne.
Biggar extended the lead with his first penalty two minutes after the re-start while Blair crashed the left-hand upright.
Things went from bad to worse for Dai Young’s men when prop Gary Powell was yellow-carded for a scrummaging offence and Biggar nudged the Ospreys further ahead with the penalty.
Then skipper Jones sealed victory with a try in the left corner just after the hour mark to leave the Blues empty-handed and still searching for their first away league win of the season.
