A freak own-goal by Lee Bullock gifted all three points to a Plymouth side who fully deserved their victory.
Once again Cardiff's failure to defend at a corner proved their downfall as Steve Crawford's 22nd minute far-post header struck Bullock on the back of the head and ricocheted into the net.
Cardiff were unchanged for the third successive game with new midfielder Jobi McAnuff signed too late to be included in the squad.
With both sides unbeaten to date there was the added incentive that the winners would top the division for at least 24 hours.
Argyle's Keith Lasley was brought down by John Robinson in the sixth minute and from the free-kick Lee Hodges had a goalbound header deflected for a corner but City cleared the danger.
With 12 minutes gone the Bluebirds had their first attempt on the visitors goal when Robert Page headed a Graham Kavanagh corner back across goal and Danny Gabbidon rose high to nod just over the Argyle bar.
Plymouth's front two, Micky Evans and Crawford, were lively and the home defence were forced to block a number of goalbound attempts.
Argyle scored the goal their early play deserved when the unlucky Bullock diverted the ball into his own net.
Bobby Williamson's side were well on top and the Bluebirds found it difficult to make any headway.
Lennie Lawrence resisted the temptation to make changes at the interval but it was still the visitors who were making all the running.
They should have increased their lead in the 56th minute when a mistake by Gabbidon left Hodges with a clear run on goal but he scuffed his shot well wide.
The unhappy Richard Langley was replaced by Paul Parry on the hour as Cardiff tried to get a bit of width into their game.
Within three minutes a Parry cross was met by Kavanagh but his first-time shot was pushed away by Luke McCormick and Robert Earnshaw hit the rebound high and wide.
City's Welsh international striker had the ball in the net in the 73rd minute from a flying header but referee Paul Taylor ruled it out for offside.
In the closing stages Plymouth's goal had some lucky escapes but they held on for a deserved victory.