USA rout Britain after nervy start in World Baseball Classic
On the game's very first pitch, Britain's Nate Eaton struck a leadoff home run off two-time reigning Cy Young winner Tarik Skubal.
A shellshocked Houston crowd booed as Eaton donned a military redcoat and a Beefeater hat amid wild celebrations in the dugout.
It was only baseball minnow Britain's fifth home run in the history of the Classic, the sport's premier international competition.
US slugger Will Smith was prevented a homer in reply in the second inning as Trayce Thompson leapt high above the right field fence for a stunning outstretched catch.
The unlikely British lead lasted all the way until the fifth inning, before Ernie Clement scored from third base on a wild pitch from newly introduced pitcher Andre Scrubb.
Phillies slugger Schwarber then immediately crushed a two-run homer to give the US a 3-1 lead and settle any nerves about a potentially seismic upset.
Gunnar Henderson drove a double to score Alex Bregman and Bryce Harper, making it 5-1, still in the fifth inning.
With bases loaded and no outs in the sixth, the US added three more runs, and then made it 9-1 in the seventh inning.
Chasing their first title since 2017, the US has assembled a "dream team" for the 20-team tournament, led by New York Yankees star Aaron Judge.
The US launched their campaign with a 15-5 victory over Brazil on Friday, while Britain lost their opening game 8-2 to Mexico.
Games are spread across Japan, Puerto Rico and the mainland United States, with the semi-finals and final to be played in Miami.