Kane Hemmings, Curtis Nelson and Toni Martinez gave Oxford United a famous and crushing victory over Newcastle United as the League One side stunned Rafa Benitez’s Championship high-fliers.

Benitez paid for his decision to make nine changes for the fourth-round tie as Simon Eastwood’s penalty save capped a fine all-round display from the Oxford goalkeeper. Eastwood won a personal duel with Aleksandar Mitrovic, following up a series of first-half saves by denying the Newcastle striker from the spot in the second half.

By then, Hemmings had already given Michael Appleton’s men the lead, maintaining his record of scoring in every round of this season’s Cup. And defender Nelson headed his first goal for Oxford to make sure of their win before Martinez capped his debut as a late substitute by heading the third.

The league remains Rafa Benitez's priority, but this heavy Cup defeat will have hurt (Getty)

Oxford began confidently and won an early free-kick 20 yards from the Newcastle goal but Chris Maguire rifled a shot into the wall. And although Benitez’s side found their feet in the moments that followed, Oxford’s defence rarely looked troubled with their forward players bold enough to trouble the visitors with their clever movement.

Marvin Johnson, the Oxford winger, gave Newcastle warning of his threat with a weaving run that was halted by a last-ditch challenge. And Newcastle defender Curtis Good set about disturbing Johnson’s rhythm moments later when he flattened the Oxford man with a hefty challenge for which he was fortunate to escape a yellow card.

Newcastle’s only early threat, meanwhile, came via a header from Aleksandar Mitrovic which went well wide. There was a let-off for the hosts on the half-hour, however, when Ayoze Perez caught a casual Chris Maguire in possession and fed Mitrovic, whose hapless tumble inside the penalty area under pressure from Curtis Nelson spared the hosts any embarrassment.

Curtis Nelson doubled Oxford's advantage with a powerful header (Getty)

Oxford, however, refused to retreat in the face of Newcastle pressure and Matz Sels in the visitors’ goal had to make a smart save at his near post to beat away a shot by Rob Hall.

Sels’ opposite number, Simon Eastwood, then had to make two fine saves to keep Newcastle at bay. The first denied Yasin Ben El-Mahanni from mid-range and the second thwarted Mitrovic in a one-on-one.

Johnson combined with Maguire just before half-time to set up John Lundstram for Oxford but his long-range effort went harmlessly wide. Eastwood then frustrated Newcastle in first-half stoppage-time when Perez combined with Jesus Gamez to feed Mitrovic but his low shot was saved smartly.

Toni Martinez came off the bench to round off Oxford's win (Getty)

Eastwood’s work was rewarded just a minute into the second half when Oxford took the lead. A cross from the right by Maguire was headed towards goal by Chey Dunkley and Hemmings forced it over the line from close range.

With just over an hour played, Newcastle had two half-chances when Hayden sent a tame header straight at Eastwood before Daniel Barlaser drilled a long-range effort narrowly wide. But they were awarded their penalty on 66 minutes when Mitrovic tumbled under a challenge from Phil Edwards, only for his poorly-struck spot-kick to be turned away by Eastwood.

Only a fine challenge from Grant Hanley prevented Hemmings adding to his earlier goal as Oxford pushed for a second. And it arrived with 10 minutes remaining as a corner from the left was headed home emphatically at the far post by Nelson. Moments later Newcastle’s embarrassment was complete as Martinez guided a header past Sels.​

Benitez defended his decision to name a much-changed starting line-up and suggested that, no matter the result, promotion from the Championship would have remained his side's sole focus.

“Experience and balance are the key if you want to be successful in the Championship because you play too many games without too much time. If we go through, we go through with the squad. If we cannot, we cannot," he said.

“We didn't take our chances in the first-half. We missed a penalty and they took theirs. We didn't mark properly at corners. You have to give credit to them. They fought for the result and we made too many mistakes.”

Appleton hailed his side's efforts, comparing the victory to that of his Blackburn Rovers side at Arsenal in this competition in 2013.

"I told them at half-time they would never get a better opportunity to reach the last 16 of the FA Cup and I told them Easty would need to make one more big save - and he did," he said. “I said before the game that winning for me would surpass beating Arsenal at the Emirates with Blackburn, and it did.

Oxford United (4-3-3): Eastwood; Edwards, Dunkley, Nelson, Skarz; Hall, Lundstram, Ledson; Maguire (Martinez 70), Hemmings, Johnson.

Subs: Agboola, Sercombe, MacDonald, Ruffels, Rothwell, Raglan.

Newcastle (4-2-3-1): Sels; Gamez, Hanley, Good, Haidara (Ritchie77); Hayden, Barlaser; El-Mahanni (Gouffran, 69), Perez, Lazaar; Mitrovic.

Subs: Elliot, Dummett, Lascelles, Shelvey, Yedlin.