LOS ANGELES — When Manager Jim Leyland walked into a news conference several hours before the start of the World Baseball Classic championship, a twinkle emerged in his eye, and a slight crease formed at his mouth.

“We’re trying to make America great again,” Leyland said as he took his seat.

It was rare sign that the United States might be having as much fun as everyone else in this tournament, given how soberly the players have carried themselves in a festive, flag-waving, bat-flipping fortnight of international baseball.

As it turned out, the Americans were just saving their fun for last, claiming their first W.B.C. title with an 8-0 rout of Puerto Rico on Wednesday night before a vibrant crowd of 51,565 at Dodger Stadium.

The United States rode six no-hit innings from pitcher Marcus Stroman, while Ian Kinsler sparked the offense with a two-run homer, a single and two runs scored in trouncing a Puerto Rico team that had entered the championship game unbeaten.