Pompey slipped to a third consecutive defeat despite taking the lead against Chelsea at the Wellington Sports Ground.
Carl WALSHE (pictured) fired the hosts ahead on 13 minutes after being given time and space to score his sixth goal of the season.
But the Londoners were soon level when Billy Clifford converted George Saville’s corner with a fine header.
Pompey had chances to retake the lead after the break but Chelsea keeper Sam Walker made a couple of fine saves to deny them.
And they were made to pay for those missed chances when Milan Lalkovic found the net with a crisp strike from 20 yards.
Todd Kane added two late goals to give the scoreline a gloss, first latching onto Bobby Devyne’s pass and coolly finishing past Matt Gledhill.
He then struck home a penalty after Perry Ryan had been shown a straight red card for bringing down the Chelsea forward in the box.
Director of youth operations Paul Smalley said: “It was an encouraging performance and we dominated large periods of the game.
“We created a lot of chances but just lacked that clinical edge and their keeper had an excellent game.
“The game was played on a difficult surface but there were good individual performances all over the pitch and the players should take a lot from the game.
“Chelsea were fortunate to win – especially so convincingly – but we have another test against West Ham next Friday to concentrate on.”
Pompey: Gledhill; Wheeler (Duyile 68), Ryan, Magri, Grant; Stockford (c) (Colson 57), Tsovolos; Gregory, Walshe, Martin (Antelmi 56); Williams
Subs not used: Seeley, Vine
Chelsea: Walker; Sampayo (c), Nkumu, Chalobah, Deen-Conteh (Nditi 46); Clifford, Rodgers; Kane, Saville, Devyne; Lalkovic (Baker 75)
Sub not used: Swift