Despite being without half of their first-choice XI, England produced a magnificent backs-to-the-wall victory against the world and European champions at Wembley on Saturday.
Walcott, who played the first half, said: "A lot of players who came in all took their chance.
"But that's what we've got in this England team. We've got so many great players in each position now.
"Tournament football, it's very important to have 23 very physically fit players and the players that came in did that and everyone's got to stay on their toes now."