Irishman Stokes, bought by Roy Keane for £2million from Arsenal, netted a blistering right-foot drive within three minutes of coming on midway through the second half.
Two minutes later, the rampant Wearsiders sealed their victory, and gained revenge for a 3-2 defeat by Argyle back in August, when David Connolly rounded off one of many flowing second-half Sunderland moves.
Although Sunderland finished on top, the game was an even affair in the first half and Argyle were denied taking the lead when Carlos Edwards cleared New Zealander Rory Fallon's header off the line following a Tony Capaldi corner.
Then Argyle's Hungarian international winger Peter Halmosi embarked on a twisting run which ended with a fierce shot that forced Marton Fulop into a full-stretch save.
Sunderland's best chance of the first 45 minutes fell to Stern John, who rose above the Argyle defence to get a head on Tobias Hysen's right-wing corner, but he was denied by an excellent save from Luke McCormick.
Argyle wasted a good chance to open the scoring within a minute of the first half when the ball fell to Fallon after a ricochet but Fulop was able to make the save.
Sunderland captain Dean Whitehead then drove the ball wide of McCormick's right-hand post before the Argyle goalkeeper made a brilliant save from Connolly's shot after good work by Edwards on the right.
Then Sunderland broke through, Stokes cutting in from the left side and unleashing a right-foot shot that beat McCormick on his inside.
Within three minutes, McCormick was again well beaten as Connolly latched on to John's cute pass and took the ball around the Argyle goalkeeper before scoring.