Match ends, Derby County 2, Chesterfield 0.
Darren Bent's first goal for Derby set up victory against a spirited Chesterfield side in a gripping FA Cup fourth-round tie.
Bent, on loan from Aston Villa, opened the scoring for Steve McClaren's Championship promotion chasers with a close-range first-half header.
But the League One visitors dominated possession and wasted several good chances after that.
Will Hughes secured Derby's fifth-round place with a late solo goal.
Chesterfield striker Armand Gnanduillet was denied by an early Cyrus Christie block, then shot tamely at keeper Kelle Roos after getting free down the left.
Bent, making his first start for Derby, struck from two yards in the 20th minute after centre-back Jake Buxton had nodded down a corner.
Chris Martin and Johnny Russell missed chances to extend the lead just after the break, while Jimmy Ryan fired over from 10 yards with the best of Chesterfield's second-half openings.
Simon Dawkins headed against the bar for Derby before Hughes made victory certain, robbing Sam Clucas outside the area and slipping past a defender before placing a right-foot shot past keeper Tommy Lee.
Derby boss Steve McClaren:
"We knew the game would be open and we were fortunate to go 1-0 up. At half-time we had to change and we tried a lot of things but I think we've learned a lot from that game.
"I'm just pleased that we came through the ups and downs of the game and we are in the hat."
Chesterfield manager Paul Cook:
"It was always going to be a difficult game for a club from a lower tier but at the end of the day you can only look up and say, 'Did we do okay?' but as a manager I felt they did more than okay."
- 36AlbentosaSubstituted forRussellat 45'minutesSubstituted forWardat 65'minutes
- 2ChristieBooked at 80mins
- 8HendrickBooked at 53mins
- 19HughesBooked at 90mins
- 9MartinSubstituted forDawkinsat 70'minutes
- 8RyanSubstituted forBanksat 75'minutes
- 10O'SheaSubstituted forGardnerat 75'minutes
- 9GnanduilletSubstituted forDieseruvweat 88'minutes
- David Webb
- Shots on Target
Second Half ends, Derby County 2, Chesterfield 0.
Will Hughes (Derby County) is shown the yellow card.
Foul by Will Hughes (Derby County).
Dan Gardner (Chesterfield) wins a free kick in the defensive half.
Corner, Derby County. Conceded by Sam Hird.
Jeff Hendrick (Derby County) wins a free kick in the defensive half.
Foul by Eoin Doyle (Chesterfield).
Jeff Hendrick (Derby County) wins a free kick on the left wing.
Foul by Tendayi Darikwa (Chesterfield).
Attempt missed. Eoin Doyle (Chesterfield) right footed shot from the centre of the box is just a bit too high.
Substitution, Chesterfield. Emmanuel Dieseruvwe replaces Armand Gnanduillet.
Attempt blocked. Armand Gnanduillet (Chesterfield) right footed shot from outside the box is blocked.
Foul by Richard Keogh (Derby County).
Armand Gnanduillet (Chesterfield) wins a free kick in the defensive half.
Attempt saved. Charlie Raglan (Chesterfield) header from the centre of the box is saved in the centre of the goal.
Corner, Chesterfield. Conceded by Cyrus Christie.
Goal! Derby County 2, Chesterfield 0. Will Hughes (Derby County) left footed shot from the centre of the box to the bottom right corner.
Cyrus Christie (Derby County) is shown the yellow card.
Foul by Cyrus Christie (Derby County).