Oxford boss Michael Appleton rated his League One team's stunning 3-0 win over Newcastle as his biggest personal achievement in the FA Cup.
Kane Hemmings put the hosts in front early in the second half before Magpies striker Aleksandar Mitrovic saw his penalty saved by man of the match Simon Eastwood. Curtis Nelson and Toni Martinez made sure of the result with further goals for the hosts.
"For me personally, with the squad Newcastle have got, this surpasses beating Arsenal at the Emirates when I was at Blackburn (in the fifth round four years ago)," Appleton said. " That's how big this is.
"This feels fantastic. It won't be long before Newcastle are plying their trade in the Premier League and, with the squad they've got, they'll be challenging in the top half, I believe.
"We tried to press really high and we had to be brave. We rode our luck at times but it was a fantastic performance.
"It was when we got the second goal that I felt we were going to do it.
"The save from the penalty probably gave the players more belief that we could win the game than if we'd got a goal then - it was massive."
Appleton continued: "Eastwood (earlier) had to make two very, very big saves with his feet (from Mitrovic).
"I said at half-time to the players, 'You won't get a better chance to get into the fifth round'.
"Kane Hemmings wasn't going to play, originally, but there has been interest from a club for Ryan Taylor so he got his chance. To be fair, the cup competitions have been good for Kane. I still want him to score more goals in the league, which I am sure he will."
Martinez's goal came on his debut, and Appleton predicted a big future for the youngster.
"Toni's got a hell of a career ahead of him," the Oxford manager said. "He's just turned 19."
Newcastle boss Rafael Benitez made nine changes, which he indicated afterwards was to protect his club's promotion push.
"We didn't take our chances in the first half, then we missed a penalty," said the Spaniard, whose side sit second in the Championship table.
"And we didn't mark properly at corners. We paid for the first mistake in the second half.
"I feel sorry for our supporters because we wanted to go through in the cup.
"Mitrovic was working hard for his chances. I was not thinking of playing him for 90 minutes but he was getting the chances. He was unlucky.
"We had our chances but we didn't take them."