A note underneath the records page on the Davis Cup website says, “Players must now be 14 or over to participate in the Davis Cup.” But Nick Imison, an I.T.F. spokesman, said that it was likely that an exception was made to allow De Rossi to play, since he was almost 14. But he did not know if San Marino requested the exception or if De Rossi’s date of birth simply slipped past whoever was supposed to notice it.

De Rossi, who recently earned his first ATP point and now has a world ranking of 1,774 and a career Davis Cup record of 7-13, saw no problem and was proud to have the record, saying, “2011 was considered my 14th year, so I guess it was O.K.”

When he returned to his middle school classroom after his first Davis Cup tie, played in Macedonia, there was little fanfare. After all, one of his classmates had already competed on the national soccer team in a World Cup qualifier.

Situated on the slopes of Mount Titano on the Adriatic side of Italy, San Marino is the world’s fifth-smallest country, with about 32,000 residents and only eight tennis courts.

“These things are not unbelievable here,” Lombardini said. “Everyone in San Marino has a great chance to break records.”

Yaka did not pick up a tennis racket until he was 29. A year later, he was the top player in Togo, a West African nation that has not competed in Davis Cup since 2003 because of a lack of resources.

Image Vittorio Pellandra, who made his Davis Cup debut in 2007. Now 75, he still plays doubles twice a week with friends. Credit... San Marino Tennis Federation

At 60, Yaka played doubles during a Davis Cup round-robin match in Mauritius in 2001, after another player had overslept and missed his flight. It was a straight-sets loss, but his opponents told a reporter in 2010 that Yaka played well and even won over the local crowd.