Chris Maguire salvaged a 1-1 draw for the Owls with a superb last-minute strike.
He sidestepped a defender and from 25 yards fired home a shot that went in off the post.
Hamza Bencherif gave Chesterfield a 29th minute lead, rising unchallenged to connect with a left-side cross from Gary Roberts.
There had been an early half-chance for Wednesday debut-maker Atdhe Nuhiu and a clearer opportunity for Paul Corry, who also headed a Jermaine Johnson cross wide early in the second half.
Wednesday trialist Kamil Zayatte was on the bench after playing in three friendlies as Dave Jones gave a run-out to last season’s centre-back partnership of Anthony Gardner and Miguel Llera.
Nuhiu, signed yesterday on a free transfer after leaving Rapid Vienna, made a half-chance for himself in the 10th minute, driving a left-foot shot into the side-netting.
Right back Liam Palmer played a one-two with Chris Maguire and set up an opening for Corry, whose shot went straight to the keeper.
Maguire was on the right side of the Owls midfield, with Corry on the left, and Johnson up front with Nuhiu.
Chesterfield included former Wednesday players Drew Talbot and Ritchie Humphreys and gave a good account of themselves.
Tommy Lee saved a far=post header from Nuhiu, who was not expected to play the whole game and was replaced by Gary Madine soon afterwards.
Corry was taken off and there was a debut on the left side of midfield for academy player Charlie Dawes, who scored for the Owls under 21s in a 1-1 draw with Barnsley team AFP yesterday.
Wednesday lacked a cutting edge and it was Chesterfield who came closest to scoring the next goal when sub Eoin Doyle headed over the bar.
Sub Armand Gnanduillet wasted a good opening, but Maguire made no mistake.
SPIREITES: Lee, Talbot, Edwards (Brown 70), Hird, Humphreys, Darikwa (Gnanduillet 87), Togwell, Ryan (Thomas 83), Bencherif (Devitt ht), Roberts, Richards (Doyle 61). Unused subs: Chapman, Smith.
OWLS: Kirkland, Palmer, Llera, Gardner, Floro, Maguire, Semedo (McCabe 76), Coke (Lavery 74), Corry (Dawes 66), J Johnson (Prutton 73), Nuhiu (Madine 66). Unused subs: Davies, Dawson, Taylor, Zayatte.