Strikers no match for defending champions.
It was the first meeting between the clubs since 2005 and Cardiff, bidding for another venture in the Women's Uefa Cup next season, never let the Newport side off the hook under the floodlights of Treforest FC.
Gwennan Harries got the champions off to a good start driving a shot through a melee of players after only 10 minutes.
And Harries doubled her tally, when she netted from close range after 18 minutes after Cardiff midfielder Kelly Isaac saw a thunderous strike crash down off the cross bar.
The Cardiff midfield were controlling the game and reducing Newport to half chances.
Their best effort came from Kirsten Davies, but her shot sailed over the bar.
Isaac and Jessica Fishlock were commanding in midfield and set up chances for Ruth Waghorn and Claire Davies.
Eventually the pressure told and Harries completed her hat-trick when she hammered the ball past the despairing keeper from a Fishlock pass.
With Cardiff dominating the game, sweeper Sian Cheedy, was denied a goal.
She strode down the right wing and thundered a shot against the underside of the crossbar.
Cardiff rang the changes after the break with Dana Hinton coming on for Terri Beddows and Natasha Harding making her senior first team debut up-front, replacing Harries.
Issac then wrapped up the scoring when she slotted the ball home from another perfectly-weighted pass from Fishlock.
Marie Barrow made a long awaited return to action having missed the last seven weeks with a foot injury.
She replaced Claire Davies for the last 20 minutes.
Several chances went begging for Cardiff with Harding, Barrow and Chantelle Miller missing efforts on goal and the game fizzled out having been won in the first hour and the bitter cold setting in.
Cardiff have now won a record 17 successive matches in the Welsh Cup and travel to face Bridgend Town in the next round on Sunday, February 18.
Bridgend beat Pontypridd in the previous round and this will be the first clash between the two South Wales teams.
Cardiff's league match with Charlton Athletic, scheduled for that day will now be rearranged for April 29.