Ipswich maintained their remarkable unbeaten record at Pride Park when a Callum Connolly header gave them a 1-0 victory over Derby.
Connolly's early strike was enough to give Ipswich their seventh win in 10 games stretching back to 2006 and although Derby pressed hard in the second half, they could not break through.
Derby came into the game on the back of two consecutive wins but Ipswich went ahead in the fifth minute when Connolly's glancing header from a corner struck the underside of the bar and crossed the line before Scott Carson clawed the ball out.
Ipswich threatened again in the 16th minute when they broke quickly with Grant Ward setting up Connolly in a central position just outside the box but this time his shot struck a defender.
The visitors were working hard to deny Derby space but the home side fashioned their best opening when Curtis Davies made a run from defence before playing in Tom Lawrence on the left, and his cross to the back post was volleyed over from 12 yards by Andreas Weimann.
Ipswich knew about the threat Lawrence posed after his successful loan spell with them last season and in the 33rd minute he went over in the penalty area only to be booked by Scott Duncan for diving.
But Derby were starting to look dangerous and Matej Vydra's clever back-heel sent Weimann in only for Bartosz Bialkowski to race off his line and dive on the ball.
Davies headed a corner at the keeper as Derby finished the half strongly but Ipswich had another opening at the start of the second when Connolly was given space at the back post but could not squeeze the ball past Carson.
Derby almost equalised in the 50th minute when they broke quickly and Weimann and Vydra combined to set up Tom Huddlestone, whose shot took a deflection but was brilliantly saved by Bialkowski.
Martyn Waghorn fired just wide at the other end before Vydra turned and sent a low shot skimming narrowly off target as Derby produced the urgency missing in the first half.
Bialkowski pushed out a Vydra free kick after Lawrence was tripped and Vydra had another free kick deflected just wide as the pressure built on Ipswich.
Derby were stretching the visitors and in the 84th minute Vydra went through after a quick passing move but could not direct his shot on target and Ipswich had another escape when Joe Ledley ballooned a shot over at the back post.
Vydra just failed to connect with a cross in stoppage time but Ipswich hung on for another memorable victory at Pride Park.