The Three Lions lost the reverse fixture 2-1 at Wembley Stadium back in September after conceding two first half goals.
"If you look at England's players coming through, there's a lack of understanding about what controlling a game is and that can really influence the tempo of a match and make a game move at the pace they want it to".
"We used the ball well against a very good team, so very pleased with it".
"There would be more concern if we weren't creating chances. We have to keep getting in those situations".
Southgate said: "The first half was pretty even but we had a very good chance from a corner, which we probably should have got on the end of".
At 18 years and 201 days old, Sancho is second only to Manchester United legend Duncan Edwards, who was 18 years 183 days old when he made his debut for England in 1955.
"I was really pleased he was in the areas to get those chances and, with his general performance as the game went on, he looked more and more of a threat", he said.
Mario Mandzukic scored the winning goal to end England's World Cup dream in Moscow, but without the Juventus striker, who has since retired from global football, Croatia lacked a focal point up front.
Frankly, they are one of the best two or three teams in the world and it's only that the coach [Julen Lopetegui] left on the eve of the summer tournament that meant they didn't fulfil what they should have done.
"I couldn't ask for more from the players".
England, who also had a weak penalty shout rejected for Mateo Kovacic's clip on clubmate Ross Barkley, introduced Jadon Sancho for the final 12 minutes. We just have to make sure we finish the chances.
England's Jadon Sancho, Borussia Dortmund's exciting 18-year old winger, produced a darting run late on after coming off the bench to replace Raheem Sterling and make his global debut before the match fizzled out in the final few minutes.
"When you walk out and the national anthem is on and you're singing it to no-one - hopefully it's something we don't have to experience too many times in our career".