England survived an early scare to mount an impressive comeback and outclass Montenegro in Podgorica, in a game overshadowed by racist abuse directed at visiting players.
Manager Gareth Southgate gave first starts to youngsters Declan Rice and Callum Hudson-Odoi but England was stunned after only 17 minutes when Marko Vesovic gave Jordan Pickford no chance with a precise, curling finish.
The visitors kept their composure to respond emphatically with confidence, class, and power by taking maximum points - and 10 goals - from their first two Euro 2020 qualifiers.
Everton defender Michael Keane headed home Barkley's free-kick for his first international goal on the half hour before the midfielder turned in Chelsea team-mate Hudson-Odoi's shot to give them the lead before the break.
Montenegro posted only a fleeting threat and Barkley effectively wrapped up the victory with a powerful finish after determined work by Raheem Sterling on 59 minutes.
England emphasized their vast superiority when Sterling was provider once more for Harry Kane's simple finish before the Manchester City forward got on the scoresheet himself.
However, the victory was marred by an unsavory conclusion with Sterling clearly responding to taunts from the home fans in his goal celebration, and Hudson-Odoi having to retrieve an object thrown on to the pitch.
And the Montenegro supporters also directed chants at Danny Rose after the defender was shown a yellow card late on, casting a shadow over another great night for Southgate and his team.