Arsenal manager Mikel Arteta explained his reasons for not playing Nicholas Pepe or Gabriel Martinelli against Benfica.
The Gunners progressed to the last 16 of the Europa League by winning 3-2 on the night and 4-3 on aggregate.
They had to come from behind in the game to secure the result.
Asked why he did not bring on Pepe or Martinelli when they were behind in the second half, Arteta told reporters: "Because there wasn't much space to run in behind, it was a really tight two lines, 4-4-1-1, or 5-3-2 at times, they were a really, really low block, not much space to run apart from when they set the line around the 18-yard box.
"You need people to unlock that, with special qualities in tight spaces to create movement and I think Willi [Brazilian winger Willian] was really helpful tonight."
