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 posed 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 emphasised 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 unsavoury 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.
Meanwhile Olivier Giroud became France’s third highest goalscorer of all time as he scored in an easy win over Iceland.
Samuel Umtiti put the hosts ahead with a glancing header from Kylian Mbappe’s left-wing cross, before Giroud saw the ball bounce off him and into the net following Benjamin Pavard’s cross.
Mbappe added a third from Antoine Griezmann’s pass, before Griezmann netted a fourth shortly afterwards.
Giroud, 32, has now scored 35 times in 89 international appearances.
The Chelsea striker’s 68th-minute goal had a touch of fortune about it as Pavard’s cross was palmed out by Iceland goalkeeper Hannes Halldorsson hit Giroud and went in.
Nevertheless, the goal took him clear of David Trezeguet’s total of 34, with only Michel Platini (41 goals in 72 appearances) and Thierry Henry (51 goals in 123 matches) ahead of him.
And in Portugal Forward Cristiano Ronaldo went off injured as Portugal drew their European Championship qualifier against Serbia.
Ronaldo pulled up with what appeared to be a hamstring injury when sprinting after the ball and was substituted in the 31st minute.
Serbia led at the time after Dusan Tadic’s early penalty but the hosts equalised through a spectacular 25-yard strike from Danilo Pereira.
Euro 2016 winners Portugal have begun their defence with two draws at home.
They were held to a scoreless draw by Ukraine on Friday.
Portugal thought they had a penalty when the referee pointed to the spot after the ball hit the outstretched arm of Antonio Rukavina from Andre Silva’s close-range header.