Substitutes Lewis Coombes and James Golby scored late goals for Argyle Under-18s in an impressive, if unexpected victory over FA Youth Cup holders Chelsea, at Cobham.
The Surrey success was the junior Greens' second successive 2-1 win over Premier League Academy opposition, after their triumph at West Bromwich Albion.
Argyle assistant youth coach Kevin Nancekivell said: "We weathered the storm in the first 20 minutes and needed Ollie Chenoweth to produce three fantastic saves.
"Once we got through that we found our feet and gradually imposed ourselves.
"The second-half was very even. We looked bright and threatened as much as Chelsea and, in the end, got our reward."
Nancekivell added: "I have to say the attitude and application of the lads in the first two weeks of pre-season has been absolutely outstanding."
The Pilgrims had to survive an opening blitz from the Blues' youngsters during a one-sided first 20 minutes.
They emerged unscathed due to some wayward shooting from the home forwards and three fine saves from goalkeeper Chenoweth.
First-year professional Chenoweth, 18, from Liskeard, was playing his first pre-season match action after being omitted from the senior squad's trip to the Netherlands.
The powerful defending of centre-back Curtis Nelson and ball-winning attributes of midfielder Jordan Berry came to the forem, as the Greens began to turn the tide.
Right-back Jack Stephens, left-winger Jake Baker and striker Matt Rickard all threatened to open the scoring. And, on the stroke of half-time, centre-back Sam Sawyer sent a header from a right-wing free kick thudding onto the Chelsea crossbar.
Midfielder Jordan Copp and Rickard went close to breaking the deadlock early in the second half, but the Greens had to wait until the 81st minute to pierce the home rearguard.
Second-year apprentice Coombes, who lives in Lipson, drifted to the near post to sidefoot a right-wing corner from Copp into the net.
Three minutes later Argyle doubled their advantage when Sawyer set up Golby, a 16-year-old trialist from Somerton in Somerset, to coolly lob the home keeper from 20 yards
Chelsea pulled one back a minute later from the penalty spot, after Nelson was adjudged to have brought down his opponent, but it was too little too late to deny the cock-a-hoop Pilgrims.
Next up for the young Greens are games against two Championship Academy sides — at Watford, on Thursday, at their London Colney training ground (1pm) and on Saturday at Reading at their Hogwood Park training complex (11am).
Argyle: Ollie Chenoweth, Jack Stephens, Connor Clifford, Dan Hart (Jordan Copp, 46), Curtis Nelson, Sam Sawyer, Jed Harper-Penman, Jordan Berry (Tom Hurley, 67), Matt Rickard (Lewis Coombes, 67), Jared Sims (James Golby, 60), Jake Baker.