Stones 'must win duels' to become world-class

England defender Stones found the net with two powerful headers as City thrashed Dutch champions Feyenoord 4-0 in Rotterdam on Wednesday to send a message of intent to their European rivals.

After a stuttering progression through the group phase last year, Guardiola was delighted at the strong start.

"Last season we were not able to win one game away (in the group stage)," he said.

"If you want to win, you have to beat them at home."

Hard-working midfielders Bernardo Silva and Kevin De Bruyne punched holes in the Feyenoord defence on a stormy evening at a packed De Kuip.

Sergio Aguero followed up Stones' opener to make it 2-0 after 10 minutes when he hammered in a half-volley from a Kyle Walker cross.

Gabriel Jesus finished off the game as a contest with a tap-in on 25 minutes before Stones' blistering second-half header from a finely-floated De Bruyne corner.

Guardiola said while Stones' attacking threat was valuable, his main job remained improving his defensive play.

"John Stones, there is no doubt about his quality," he said.

"But he knows what the gap is to improve as a football player, he has to win the duels.

"When he will be able to do that he will become an exceptional central defender."

City's next European hurdle is a home clash against Shakhtar Donetsk, who beat Napoli 2-1 in their opener, on September 26.