Chesterfield left the best to last tonight - with two goals in extra time to ensure a fourth round FA Cup tie at Derby County.
They had been hosting on Scunthorpe, after tying their first game 2-2 away in the third round.
Tonight’s game was watched by Steve McClaren the Derby boss who was awaiting the victor.
He saw Sam Clucas score two late goals to seal their derby date.
Visiting goalie Sam Scalemen - who defied the Spireites so well last week did just the same straight from the off, stopping Tendayi Darikwa in the first exchange.
At the other end Gary McSheffrey had an effort charged down.
On 19 minutes, Armand Gnanduillet tested Slocombe again with a near post drive, which was parried.
Ten minutes later, Romuald Boco almost opened the scoring but the ball was blocked en route.
On the hour, Scunthorpe cashed in on some sloppy midfield play and Paddy Madden smashed the ball just wide.
Slocombe then confounded the home side again: the goalie dealing well with a dangerous Eoin Doyle cross.
On 81 minutes, Spireites made a change. Jimmy Ryan came on for Ritchie Humphreys, triggering a wave of applause for the veteran.
There was to be no breakthrough in regular time and Dan Jones came on for Boco in extra time.
Lyle Taylor had Tommy Lee in some trouble but his defenders reacted fast to get the ball away.
Chesterfield broke through eventually through Clucas.
In the 105th minute, the 24 year old from Lincoln ably finished off a nice passing move.
The Iron almost levelled a minute later, Alex Davey, who won the corner, heading the dead ball over the bar.
Davey then had a back-heel attempt collared by Lee, as the first flakes of snow started to fall at the Proact stadium.
The tie was put beyond doubt though when Clucas made it a double for the night, on 116 minutes.
He profited from a decisive piece of wing play from Darikwa, allowing himself just enough time to bend it past Slocombe.
Chesterfield: Lee; Darikwa, Hird, Raglan, Clucas; Boco, Morsy, Humphreys, Roberts; Gnanduillet, Doyle.
Subs: Wright, Jones, Evatt, Ryan, O’Shea, Gardner, Beresford.
Scunthorpe: Slocombe, Davey, Boyce, Llera, Williams, Osbourne, Bishop, Nolan, McSheffrey, Madden, Taylor.
Subs: Weaver, Adelakun, Canavan, Hawkridge, Wooton, Sparrow, Mosanya.
Ref: Keith Hill (Hertfordshire)
Attendance: 6,815, (331 away fans.)