Arsenal boss Arsene Wenger admits his players had to work hard to battle past Burnley in the FA Cup.
The Gunners were far from their best against Sean Dyche's determined team but still managed to reach the fifth round of the competition after a 2-1 win.
"We needed to work," Wenger explained.
"At the start it looked like it would be easy because we had a lot of the ball and good opportunities around the box. When it came back to 1-1, it became a different game.
"I think we were a bit shocked and they gained belief. I saw them against Derby and I could see that this is a very efficient, strong team with no weakness.
"Everything they do is based on efficiency and they've shown that today. In the second half, I don't think they created a lot. They had one or two opportunities on the counter-attack but we managed to win the game and we looked quite in control at the end. We needed to keep our focus, our urgency until the last minute."
21-year-old Calum Chambers scored one of the most beautiful goals for Arsenal this season and the 66-year-old was full of praise for the youngster after the game.
"[The two goals?] I would say they are two completely different goals.
"One came from a build up in the final third, where we were patient and moved the ball well, with great finishing from Chambers. He's quite a good finisher in training.
"The second one was in transition, coming out quickly from the back and finishing well, with a lot of pace. They were two completely different goals."
Asked about the fitness level of attacking midfielder Alexis Sanchez, Wenger added: "[It was Alexis' first start] for eight or nine weeks.
"When I saw Derby against Burnley, I had a little hesitation to pick the three [Alexis, Coquelin, Elneny].
"But the fact that we played at home, I thought we could manage to get away with it. With Alexis, I was not too much worried about on the fitness front because I kept him out two weeks ago and he was already there physically.
"We had some worries about his muscle but today he came through well and you could see that physically, he is ready."
