Hylton thought he had netted his 18th goal of the season to close the gap further, but a late offside flag allowed Newcastle to see the game out safely.
"I said in the news conference we wanted to approach the game with a strong team to make sure we were going through," Benitez told reporters. "First half we finished really well. We were 3-0 up, maybe it's harder to keep concentration in the second half.
"They scored and maybe had belief they could then score more. We had chances to finish the game. The first half was quite good, a lot of possession, passing and good goals.
"In the second half we needed more experience to manage these games. Keep the ball and then a fourth goal would have finished it but we couldn't do it."
Next up for Newcastle is a home Premier League clash with Swansea City next weekend.