MONTERREY, Mexico —The convenience store was the last stop until the border on the road leading out of this industrial Mexican city, and Raul Vargas, a tour guide, made his instructions clear: the 24 die-hard Cowboys fans on his charter bus should get their snacks and beer now, because this bus would not stop again until it reached the United States Customs checkpoint in Laredo.

The sun had set an hour ago, and Mr. Vargas did not have to say what his passengers already knew: traversing these Mexican highways — especially after dark — could mean a run-in with the country’s fiercest drug cartels.

For these travelers, who ranged from blue-collar construction laborers and freight-line managers to lawyers, professors and engineers, the chance to watch America’s Team play in the new Cowboys Stadium was worth the risk, and the $400 round-trip fare. Their weekend trip to Texas included visits to a 160-acre flea market in Grand Prairie, a giant shopping mall in Arlington and an overnight stay at a hotel with a complimentary happy hour.

But it was the final stop, to watch the Cowboys face the Giants, a division rival intent on taking the Pokes’ first-place standing, that had been marked on their calendars for months.