Goals from Sam Edozie, Ben Knight and Riyad Mahrez saw City go in at half-time 3-0 up after a blistering first 45 minutes.
And with Kevin De Bruyne watching on from the stands, Nathan Ake fired in City's fourth after a clever backheel from Pablo Moreno in the second half.
It was a fine performance from City, with Pep Guardiola blending youth and experience expertly to see off a side who finished fifth in the Championship last term.
City were on the front from the off, with plenty of verve and vitality to our pass-and-move, possession-based football.
Sam Edozie opened the scoring with a tap in at the backpost after wonderful play from Riyad Mahrez down the right, the Algerian playing a pinpoint ball across the six-yard box to present the youngster with a simple finish.
It was Edozie’s second goal in two games after he bagged in Tuesday’s 2-0 win at home to Preston.
Ben Knight doubled our lead after more good work down City’s right, this time Mahrez setting Joao Cancelo free with a beautiful pass, allowing the Portuguese full-back the time and space to pick out Knight, who finished confidently.
It was a brilliant move - swift, creative and ruthless - and it was clear City were hitting top gear.
Our third was created down the left, with Benjamin Mendy swinging in a fine cross from deep that saw Mahrez finish expertly on the half volley.
Cole Palmer then produced an outrageous piece of skill on the byline to beat Jasper Moon, but the Barnsley defender pulled back the City youngster and a penalty was awarded. Palmer stepped up and took the spot kick himself, but Bradley Collins guessed the right way and made a decent stop to keep the ensure his side went in at half-time 3-0.
City made a raft of changes at the break, including introducing Ilkay Gundogan and Oleksandr Zinchenko, both of whom returned to the CFA this week after their exertions in this summer's European Championships.
Nathan Ake powered home from inside the six yard box add further gloss to the scoreline and seal our second pre-season victory of the week.
After curling in a fine free-kick during Tuesday’s victory over Preston, Riyad Mahrez dazzled once again.
His first decisive moment saw him deliver a fine first-time cross from the right to set Sam Edozie up for the opener, before playing a superb outside-of-the-boot pass to set Joao Cancelo free down City’s right in the build up to Ben Knight’s goal that made it 2-0.
And his first-time finish from Benjamin Mendy’s deep cross made it 3-0 to offer another example of his world-class finishing ability.
His touch and technique are superb, and he looks like heading into the new season fresh and very much in form.
Covering tackles, bravery, excellent passing and general leadership, Ruben Dias is a complete centre-half.
After making such a significant impact last season, bringing solidity to City’s backline and forming a fine partnership with John Stones, he will be desperate to kick on again this term.
He was superb against Barnsley, a beacon of calm and such an intelligent reader of the game.
He only played the first half, making way at the break for Phillipe Sandler, but he is a pleasure to watch and a clear leader in Pep Guardiola’s side.
"They tried to play and we created chances and played very good.
"We have loan players, young players. We tried to give minutes as much as possible to our players because in seven days we play the Community Shield.
"Half an hour for Alex and Gundo today - this is good.
"We are far away still, but this is normal. We have a lot to improve. Tomorrow training, Tuesday game and then prepare the final."
City XI: Steffen, Cancelo, Dias, Ake, Mendy, Fernandinho, McAtee, Palmer, Knight, Edozie, Mahrez
Subs: Van Sas, Gundogan, Zinchenko, Sandler, Roberts, Couto, Moreno, Pozo, Rogers, Bolton, Gomes, Diounkou, Burns
Barnsley XI: Collins, Styles, Kitching, Brittain, Woodrow, Morris, Moon, Palmer, Oduor, Frieser, Helik
Subs: Walton, Williams, Benson, Halme, Sibbick, Ritzmaier, Miller, Thompson
City will host Blackpool on Tuesday in our third pre-season friendly of the summer.
The game will be played at the Academy Stadium, with kick off at 18:00 BST.
Once again, CITY+ subscribers can watch every kick live.
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And then next Saturday, we face Leicester City at Wembley Stadium in the Community Shield, the traditional curtain-raiser ahead of the new campaign.
That game gets under way at 17:15 BST and we will bring you live text updates right here on ManCity.com from 15:15.
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