Marcus Rashford and Barkley had Gareth Southgate's men two goals to the good midway through the first half when play was stopped and a message relayed over the public address system at Vasil Levski National Stadium, urging home supporters to cease their abuse.
In between Barkley and Sterling continuing an emphatic response to the Three Lions' surprise defeat to the Czech Republic, there was a further lengthy delay.
Events on the field became secondary as pre-match fears England players would be targeted by racist chants were realised.
Sterling clashed with Bulgaria winger Wanderson after being fouled by Ismail Isa Mustafa in the 25th minute and a stoppage followed, with an appeal made over the stadium's public address system urging those offending fans to desist.
It was 3-0 by the time England boss Gareth Southgate entered conversation with the fourth official, preceding another more prolonged break in play – during which a group of Bulgaria fans were ejected from the stadium.
Under UEFA's protocol for dealing with racist incidents, the next steps for match referee Ivan Bebek would be to suspend the game and send the players to their dressing rooms for a specific period and then, if discriminatory behaviour did not stop or broke out again, abandon the match.
The match appeared under threat of abandonment at that stage, as a group of fans were ejected, but England resumed their punishment of over-matched opponents – captain Harry Kane laying on Sterling's second and completing the scoring five minutes from time.