O’Shea brought an end to the Spireites’ 502-minute wait for a goal against Colchester on Saturday.
That victory and Tuesday night’s EFL Trophy win at Crewe, in which O’Shea also netted, have come at a good time for Town.
On Sunday they welcome one of the country’s form sides in the shape of Chris Wilder’s Blades.
O’Shea acknowledges how significant the fixture is: “We’ve got that big game coming up on Sunday against Sheffield United and that’s massive for us”
“(Losing 3-0) was a big disappointment last season because in recent years we’ve given them some good games at the Proact.
“So we’ll be looking to turn that around on Sunday.”
Chesterfield will be without Liam Graham for the derby clash.
The right-back is currently on international duty with New Zealand.