The Three Lions captain was expected to be rested for the clash but replaced Danny Welbeck after 61 minutes of play at the King Power Stadium.
And Southgate says there were no issues playing the Tottenham star.
He said: "I think he's going to get matches at his club. He's had three days of little training. We needed to keep him ticking over.
"If he didn't play today, he would have gone out and done some running on the pitch. Playing him for 30 minutes was no big issue. To start the game is a different sort of feel, mentally it's different. Also, we wanted to finish the game strongly. We had a real jigsaw to figure in terms of who we could play and take off."