In the final game of Group G, England lost 1-0 and broke the momentum they had built with victories over Tunisia and Panama earlier in the tournament.
Southgate concedes that a defeat on Tuesday would open him up for huge criticism over the changes he made, but it is something he accepts and is prepared for if the worst comes to the worst.
"We had to make a decision we felt gave us the best opportunity preparing the whole squad for that game and that's what we tried to do," Southgate told MailOnline Sport.
"Of course, if we don't win, I understand people would say whatever about the Belgium game, but for me that was the right thing to do and you've got to take decisions you believe are the right ones."
The Daily Mail also report that star striker Harry Kane was desperate to play in order to approve Golden Boot chances, so much so that Southgate held special talks with his captain to explain his decision.
"I felt the need to sit with him, but he was brilliant," Southgate said. "He totally understood, 100 per cent, that it was team first.
"He said 'look, I know everyone says I want the Golden Boot. Of course it's something I want to do. But the main thing is getting the team through the first knockout. He was excellent on that, showed real leadership and understanding of the big picture."
With fears that England had lost their momentum with defeat to Belgium, Southgate urged his squad to maintain positivity from Tunisia and Panama victories.
He told his players that the best teams in the world bounce back from disappointments and England need to do the same if they are to be successful
"I think whoever we played we believe we're capable of beating," he said. "Whoever we play are capable of, in a one-off game, beating us. But we had to make a decision we felt gave us the best opportunity of preparing the whole squad for that game and that's what we tried to do.
"It's exciting. For me, it's going to be a brilliant game to be involved in. They have some top players, some top attacking players in particular. But we also have some really good players who are full of belief and looking forward to this challenge."
While admitting that the blame will be on him if England falter, he has unquestionable belief in the brave decisions he makes.
"You have to be bold enough to accept that might come with questions at times," he said. "But if we believe it's the right thing to do then we stand by it."