NEW YORK — Are the Mariners for real? That’s what the Yankees are asking themselves this Sunday afternoon as they return to their clubhouse having dropped two in a row (and the series) to the upstart Seattle Mariners. What’s that, you ask? What happened in the Bronx this weekend? Well, the Mariners won their first series against the Yankees. Yes, we know. They’re an expansion team. An expansion team in a city where baseball expansion doesn’t have a strong track record. An expansion team that’s playing like you’d expect an expansion team to play. At the end of April, they sit in the cellar of the American League West. Two days ago, they were making a ten-game losing streak an eleven-game losing streak. And then they won two in a row against the Yankees. Handing the Bronx Bombers their first series loss this season. Is this a sign that the Mariners might be able to compete with the big boys this summer? There have been worse bets in baseball history (No, No, Nanette, anyone?). But maybe we’re better off enjoying this win over the Yankees on its own terms and worrying about the rest of the season later.