"From when the manager came in he told us the style of play, how he wanted us to play, how to press". We gave the ball away too cheaply and we'll have to go away and look at it.
"We tried to change the shape in the first half but it didn't work as well as it might", admitted Southgate.
The Kobra made his global debut for the Czech Republic after being subbed on in the 65th minute.
After Kane opened the scoring in the fifth minute, England looked lacklustre in attack and susceptible at the back as the alarming defending in last month's 5-3 win against Kosovo was repeated.More news: Judge blocks rule that would have kept some immigrants from legal status
The squad will remain in Prague until Sunday, when they head to Sofia for Monday night's game with Bulgaria.
"I think it was down to us". Chelsea would be the same on that, I think.
'We have to respond in the right way'.
"I don't think it's a night for positives, that's for sure". We accept defeat, and accept we have to be better than we were.
Asked how much blame he accepts having selected some out-of-form players in an ineffective 4-2-3-1 formation, Southgate said: "Yeah, look, I always have to accept responsibility".More news: Advance Polling Stations open Friday
"We started the second half a lot better and had chances, but we conceded too many poor chances and gave the ball away too many times". "But we collectively have to accept the result and, as the manager, I've got to accept that as well, absolutely".
The result means the Czechs join group leaders England on 12 points with four wins, although they have played one game more.
And after the match, Southgate was blunt with his appraisal of his team's performance.
"The performance was really great, we were active and made England sweat even though they are a very strong team".More news: Huge Brush Fire Prompts Numerous Freeway and Road Closures