The home side started the brighter and went 1-0 up on 11 minutes after Tyson tucked the ball underneath Chris Kirkland in the Wednesday goal.
Buxton doubled the lead just ahead of the half-hour mark before O'Grady struck with a curling effort from the edge of the box after 39 minutes.
Gary Medine replaced fellow new striker Nejc Pecnik just before the hour mark and he thought he had the equaliser with five minutes remaining but his strike was ruled out for a handball.
Two minutes later, the away side had the ball in the net again, but Theo Robinson had strayed offside.
As the game crept into injury time, Johnson's header sent his side away with a share of the spoils.