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The international tournament began Thursday, days before Seattle and Vancouver host their first matches.
The Mariners are 4-17 this season when they do not hit a home run.
Randy Arozarena’s go-ahead homer was the difference in the M’s extra-innings win in Baltimore.
Mitch Garver also homered for the AL West-leading Mariners, who have won 11 of their last 14 games.
The 2026 World Cup runs from June 11 to July 19 at stadiums in the United States, Canada and Mexico.
The Big Grumper’s fifth-inning grand slam was the difference as the Mariners took their series opener in Baltimore.
Randy Arozarena had three hits for the AL West-leading Mariners, who have won 10 of their last 13 games.
The Mariners will be without their veteran shortstop and leadoff hitter for at least a week.
Seattle wasted a strong start from Luis Castillo, who left with a 3-1 lead after yielding three hits in 5 2/3 innings.
J.P. Crawford led off with his 10th homer of the season for Seattle.