Grant Leadbitter admits there was relief all round following Boro's Emirates FA Cup win on Saturday afternoon but says focus going forward will be on avoiding complacency.
"We're relieved to be in the next round," said the captain. "I think there was a contrast in performance from the first to second half.
"First half was very good from the boys. We came out the traps early and the game should have been out of sight - we should have had more goals.
"Credit to Oxford, they came out second half and we made silly mistakes. We're experienced players but made silly mistakes and we let them back into the game.
"But the boys came back and are through to the next round. They scored the goal and were on the front foot. We made mistakes from the first goal.
"We have to cut out the silly mistakes, we have experienced players on the pitch but like I say the football club is happy to be in the quarter-finals.
"They don't come around often in the FA Cup and you never know, you have a chance to go to Wembley - it would be great for the fans but we have an important game next week."
Boro travel to Selhurst Park on Saturday to take on Crystal Palace who currently sit three points below in the Premier League table.
The Eagles emerged as winners when the two sides met at the Riverside earlier this season, though, and Leadbitter is looking for Boro to carry confidence into the weekend's game.
"We just look forward to the next game," he said. "That's what we do at the football club.
"At the end of the day we have to start winning a lot more football games and we need to win games to stay in the division.
"We were expected to win on Saturday. People might not give us credit but we did our jobs, you've seen other Premier League teams go out.
"So we're happy to be in the next round and hopefully it gives the boys confidence going into the next game against Palace. It's going to be tough but we're really looking forward to it."