Oxford Manager Ian Atkins had no complaints as first division Reading moved comfortably into the next round with a confident display of passing at the Kassam Stadium.
However, the Royals were given a real scare by the third division outfit when Oxford substitute Jefferson Louis headed home a Matt Robinson cross 11 minutes from time to make it 2-1.
After surviving a few frantic minutes, however, Nicky Forster settled matters when he fired home from close range in the last minute to ensure victory.
Forster had been instrumental in Reading's opener on 52 minutes, breaking clear down the left and firing in a vicious shot which Oxford goalkeeper Andy Woodman made a terrific save low to his left, only for the ball to rebound on to the thigh of John Salako and into the net.
Reading were always in control and it came as little surprise when they doubled the advantage, Forster beating three defenders before lashing home with his left foot.
Atkins was pleased with the performance of his side, but full of praise for Reading.
"Reading are a very good side and played some great football," he said.
"Their passing was exceptional and at times left us in all sorts of trouble.
"The difference between the sides was around the penalty area, the movement of Forster was different class and we don't get that at our level.
"But we played some good stuff ourselves although did defend too deep at times.
"This was the first of three games we have got at home, but it is the one out of the three that I do not mind losing because the other two are League matches and promotion is our aim this year."