The first goal came in the 8th minute, Barton tapping home after Trevor Sinclair's far-post header.
The second was shrouded in confusion as City were awarded an indirect free-kick for a backpass, although it looked like it wasn't deliberate. Paul Dickov played a quick free-kick and Barton tapped in his second in the 31st minute.
Just 9 minutes later Barton wrapped up his hat-trick. Ishmael Miller released Dickov, who held the ball up for Sinclair. The City winger then squared it for Barton to stab home.
There were then a string of substitutions in the second half, and one of the subs, Willo Flood, had the best shot of the second period, having a decent drive saved in the 78th minute.
This was City's 3rd pre-season friendly. Last week they drew 3-3 at Wrexham with Miller opening the scoring and Georgios Samaras adding two more (although one was deflected). At the other end, Sylvain Distin turned Wrexham's 3rd equaliser into his own net.
At Rochdale on Saturday, City went 2-0 down inside 12 minutes, but Samaras pulled one back 2 minutes before the break, curling home after good work by Didi Hamann and Stephen Ireland. Barton equalised with a 60th-minute penalty and Dickov gave City the win by also scoring from the spot 4 minutes later.
City team v Wrexham: Hart, Flood (D Mills), Thatcher (Jordan), Dabo (Hamann), Dunne (Distin), M Mills (Richards), Sinclair (Croft), Barton (Laird), Miller (Ireland), Sibierski (Samaras), Vassell (Dickov).
City team v Rochdale: Weaver (Schmeichel 46), Jordan (Logan 77), Richards (Flood 77), Distin (D'Laryea 69), M.Mills (D.Mills 46), Croft (Sturridge 77), Barton (Williamson 77), Ireland (Johnson 73), Hamann (Laird 65), Sibierski (Dickov 63), Samaras (Miller 63).
City team v Port Vale: Weaver (Hart 46), D.Mills, Thatcher (Williamson 70), Richards (Jordan 46), Dunne (Logan 70), Sinclair (Flood 70), Miller (Laird 70), Barton (Ireland 46), Dabo (Johnson 70), Dickov (Etuhu 70), Samaras (Sturridge 56).