Second-half goals from Harry Kane and Saido Berahino proved enough to give the Three Lions an advantage in the tie, which head coach Southgate felt was just as tough as he expected.
And with the reverse fixture to come in Vinkovci next week, he was glad to emerge with the lead at ‘half time’.
England U21s 2-1 Croatia U21s
UEFA Euro U21 Championship
Play-off first leg
Friday 10 October 2014
Molineux, Wolverhampton Wanderers
Attendance: 23,107
“It was a really good game of football to start with and it was a great test for us,” he said.
“We had to show character, quality, intelligence and, in the end, we just about passed all those tests.
“Croatia are a technically good side, physically strong, defended well and were well organised, so it was a really good result to win the game, especially from being a goal down so early.
“That’s a challenge we’ve faced before, but this is the best team we’ve faced that we’ve had to do it against.
“So I was really pleased that we showed the patience and belief in the way we play to keep probing.
“We had one or two other chances, we hit the post and we still had to defend well as they were a threat on the counter.
“But we kept passing the ball and moving the ball and I was really pleased with the character we showed.”
The winning goal came with just five minutes remaining, when top scorer Berahino was fouled in the box before despatching the penalty himself.
And Southgate praised the West Brom man’s nerve, as he took his Euro qualifying tally to nine goals in as many games.
“They’re big moments and you need character and belief, and he certainly had that and then there was a fantastic recovering tackle from Eric Dier,” he explained.
“When we talk about the importance of the group and the squad, such as the players who haven’t been here tonight but the ones who came off the bench and made a big contribution, people like Tom Ince and Eric Dier.
“That’s why you need everybody ready and involved and why they’re a pleasure to work with.”
With such a quick turnaround before the second leg on Tuesday, Southgate and his staff are now planning the squad’s routine carefully before they fly out to Croatia on Monday.
“We will recover in the morning and then in the afternoon I want them to get away from St. George’s and just relax and switch off for a bit,” he revealed.
“That’s important as it’s been a week with a lot of focus and attention, so we’ll do the right thing tonight and in the morning and then we’ll be back again tomorrow night to start honing in on the game.”
England Under-21s head coach Gareth Southgate speaks after his side's 2-1 win