Scott Wharton was back in the side after completing a three-match ban with Michael Harriman also passed fit to play after missing the win at Macclesfield. Paul Anderson and Andy Williams were also recalled with young academy striker Caleb Chukwuemeka named on the bench. Having not been available for the original tie, none of the January signings were eligible. Wayne Rooney started for Derby who named a strong side.
The Cobblers, looking to reach the fifth round for the first time in 50 years, were backed by over 4,000 travelling fans who were all in fine voice as the game got underway.
With ten minutes on the clock the Cobblers appealed for a penalty when an Andy Williams shot was blocked by Andre Wisdom but referee David Webb waved play on. Chris Lines then fired over from an acute angle before Jack Marriott went close for the Rams.
Tom Lawrence tested David Cornell from 20-yards and Michael Harriman made a vital interception to deny Chris Martin a shot on goal as Derby tried to build up a head of steam. It was a fantastic last-ditch tackle from Harriman with Wayne Rooney’s terrific pass having created the chance.
Cornell made a good save from Marriott while his opposite number Kelle Roos was forced into action by a Sam Hoskins shot that looked to be goalbound until the Derby keeper got a hand to it.
Derby took the lead from a Rooney corner just before the half hour mark, Andre Wisdom scoring from close range.
Duane Holmes then showed his pace and quality to make it 2-0, bursting through the middle and producing a composed finish.
The Cobblers were pushing forward looking for an equaliser but they were caught on the break and Jack Marriott restored Derby’s two goal lead with a header despite a terrific initial save from Cornell.
Marriott had a shot deflected wide with the Championship side now looking to put the tie to bed.
Scott Pollock and Joe Martin came on for Chris Lines and Nicky Adams before Hoskins went close to pulling a goal back with a shot deflected over.
Wayne Rooney made it 4-1 from the penalty spot, Cornell having saved from substitute Jason Knight before Tom Lawrence went down under a challenge.
Sam Hoskins then scored from the spot as the Cobblers were awarded a penalty of their own for a foul by Curtis Davies on Williams.
There were no more goals but it had been a valiant effort from the Cobblers who refused to lie down and kept pressing right until the end, Hoskins going close deep in stoppage time.