One could forgive the top soccer players in Mexico and the United States if they feel as if they have seen quite a lot of each other recently.

When some of the best players from Mexico’s Liga MX lined up against some of the biggest stars from Major League Soccer in the M.L.S. All-Star Game on Wednesday night in Los Angeles, it was not — for a handful of them — the first time they had played an important match north of the border this summer. Whether in a series of new cross-border club competitions or in two important national team tournaments, the Nations League and Gold Cup, U.S.-Mexico matchups — in a variety of jersey colors — are now more frequent than ever.