A stunning curled effort from Adnan Januzaj wrapped the game up early in the second half, with both teams making a host of changes from their previous games.
Speaking after the match, Southgate told reporters (per the Guardian) that he was looking 'at the bigger picture' with England's 'biggest game for a decade' coming up against Colombia on Tuesday.
“This was a game we wanted to win but the knockout is the biggest game for a decade for us and we had to make sure our key players were preserved,” said Southgate.
“You have to look at the bigger picture sometimes and make decisions which, in some quarters, might be criticised. But everyone understands – in the dressing room and in the group – what we’re trying to do.
“With respect, in the Euros I think we were only ahead for a few minutes of any of the games. Here we’ve played extremely well. We’ve played well in the games leading into and at the tournament, and I don’t think we’ve played poorly at all tonight.
"We don’t like losing and don’t want to lose matches, but the primary objective from the evening we’ve got. And if we’d put Harry on for 10 minutes and someone had raked his ankle, that would have been ridiculous. The knockout game is the important one."
While conceding that that he and his team have a responsibility to produce good football and positive results, Southgate stood firmly by his decision, with which he is 'entirely comfortable'.
“Of course we have a responsibility to the supporters, and the support in the stadium was absolutely outstanding tonight. The support and encouragement from home has been brilliant. But when you’re a leader and a manager, you have to make decisions which are right for your group to achieve the primary objective.
"Sometimes those decisions will be criticised. I understand that. But only one person makes that decision with all the full facts and managing a tournament in mind: physically, medically, tactically for the benefit of the group. I’m entirely comfortable with the decision. Sometimes you have to make decisions for the bigger picture.”