Greek-American baseball player Clay Bellinger scored Greece's first run of the Olympics in a 5-4 loss to Cuba.
Bellinger is an MLB star in the USA
Bellinger, who won a World Series with the New York Yankees, had never visited Greece before the Games.
But his adopted team did well to make a contest of it against Cuba, favourites to win gold in the absence of the USA.
"We are trying to give a good show and were hoping to be embraced like this," he said of the exuberant if sometimes confused welcome given by local fans.
"They have soccer cheers going on in a baseball stadium," he added. "Hopefully they will realise just how fun a sport it is to come and watch."
In other Monday games, Canada hammered Italy 9-3, Australia again had trouble scoring runs, losing to Taiwan 3-0, and Japan beat the Netherlands 8-3.