A brace for Bukayo Saka, plus goals for Jude Bellingham, Raheem Sterling, Marcus Rashford and Jack Grealish, saw the Three Lions kick off Qatar 2022 in style at Khalifa International Stadium.
But despite matching their biggest single-match haul in a World Cup game, set four years ago in a 6-1 win over Panama at Russia 2018, their manager was still left frustrated by their double concession.
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Mehdi Taremi’s double, the second of which came from a controversial VAR penalty, denied England a record winning margin, and Southgate acknowledged it added a sour note to his side’s otherwise superb performance.
“I’m a bit fed up with the end of it, really,” he told BBC Sport. “To win by that margin, to play as we did for the majority of the game, you’ve got to be really happy.
“They dealt with the game really well. It was a sticky first half with lots of stops, but we were a real threat throughout. Our movement was really good.
“But we shouldn’t be conceding two goals [at] that stage of the game. We’ll have to be right on our game against the United States, it was a great start, but we will have to do better.
“It’s a consequence of the scoreline a bit. We just lost concentration and when we play at a slower tempo, we’re nowhere near as effective.”
Southgate’s win takes him to nine at major tournaments, past Alf Ramsey’s record of eight, while Bellingham and Saka’s goals saw two players under 21 score in the same World Cup game for the first time in England history.
With five different goalscorers overall, the Three Lions boss was delighted with their involvement, adding: “We’ve got some good players, and today they really delivered. It’s a great marker to put down.”
In particular, Southgate credited Callum Wilson’s assist for Grealish to grab his side’s sixth of the match, while warning he must keep his players rooted to the ground ahead of further stern tests.
“Wilson was on,” he added. “He could have been selfish but he was thinking of the team even at that moment. I should be more excited, but I’ve got to keep the team on the right track, where we have to be better.”