Three years on from their heartbreaking extra-time loss at the Luzhniki, the Three Lions exacted some sort of revenge by triumphing in the Group D opener at a pulsating, partially filled Wembley.
Sterling could see the stadium from his house growing up and scored under the arch that is etched onto his arm, securing a 1-0 win against Croatia on a sweltering Sunday afternoon in the capital.
Mount was a whisker away with a 25-yard free-kick and Sterling looked frustrated after lashing over from a Tyrone Mings knockdown as England looked to rubber-stamp victory.
John Stones was able to run off a knock and Southgate introduced 17-year-old Jude Bellingham for the closing stages; he became the youngest player to feature in Euros history.
England had to dig deep and contain Croatia until the end but they held on for the narrow victory, with Southgate's delight clear after a late miss for the visitors was followed by the final whistle.