Newcastle United were two up at half-time at Oxford with the fifth round in sight.
Sean Longstaff scored an excellent long range opener before Joelinton dispatched a second – minutes before he went off injured with a hip problem.
It put the Magpies in a commanding position after 45 frenetic minutes at the Kassam Stadium.
In front of a watching Mike Ashley, a strong Steve Bruce side struck early against their League One opponents. But after Joelinton’s second, Oxford made chances of their own and Karl Darlow and Jamaal Lascelles both denied Oxford.
Here are Lee Ryder’s player ratings.
Karl Darlow 7
Made a vital save to deny Jamie Mackie.
DeAndre Yedlin 7
A couple of decent forays up the right.
Jamaal Lascelles 7
A vital clearance off the line as Oxford threatened to get back into the game.
Fabian Schar 6
Steady enough shift so far.
Florian Lejeune 6
Safety first needed at first as Oxford gave him a rough time.
Matt Ritchie 7
Gave Oxford problems down the left-hand side.
Sean Longstaff 8
Really went about his business with intent. A fantastic strike to put United ahead.
Matty Longstaff 7
Played it with the spirit the FA Cup demands.
Nabil Bentaleb 8
Some sizzling plays forward - not least to set up Joelinton for the second goal.
Miguel Almiron 7
Some excellent bursts forward but should have finished the tie on 37 minutes when he stabbed wide.
Missed an early chance but bounced back to finish well after being set free by Bentaleb. A much-needed goal but he limped off injured before the break.
Allan Saint-Maximin (for Joelinton 36)