Hall found Tabb with his back to goal 25 yards out and he returned the ball to the defender, who headed back to Tabb who in turn found John.
Ian Westlake came closest for Leeds when he forced Andy Marshall to dive to his right to parry a curling shot.
Leeds manager Kevin Blackwell:
"Yes, it's another defeat and that's what the record books will show but as on many occasions this season it just wasn't our day.
"But we can take encouragement from our second-half performance.
"Had Geoff Horsfield scored when he was through then it could have been a different story.
Coventry: Marshall, McNamee, Page, Ward, Hall, Birchall, Hughes, Doyle, Tabb (Cameron 74), Kyle (Hutchison 88), John (McKenzie 69).
Subs Not Used: Adebola, Thornton.
Booked: Kyle, Tabb.
Goals: John 26.
Leeds: Warner, Kelly, Butler, Kilgallon, Crainey, Carole (Stone 69), Nicholls, Gregan (Douglas 45), Westlake (Blake 85), Healy, Horsfield.
Subs Not Used: Lewis, Moore.
Booked: Butler, Kilgallon, Crainey.
Att: 22,146
Ref: I Williamson (Berkshire).