The ATP Cup has gotten off to an awkward start with the wrong national anthem played for Moldova before the country's opening clash with Belgium in Sydney.

Key points: The ATP Cup apologised for playing the Romanian anthem instead of the Moldovan anthem before the match in Sydney

The ATP Cup apologised for playing the Romanian anthem instead of the Moldovan anthem before the match in Sydney The Romanian national anthem was the Moldovan anthem briefly after the fall of the Soviet Union

The Romanian national anthem was the Moldovan anthem briefly after the fall of the Soviet Union Moldova went on to lose their ATP Cup tie with Belgium 3-0

Organisers apologised to Moldovan officials after the anthem for their eastern European neighbour Romania echoed out over Ken Rosewall Arena on Friday.

"At the start of the Moldova vs Belgium match we mistakenly played the wrong national anthem for Moldova," a statement on ATP Cup's Twitter account read.

"We are sincerely sorry and have apologised personally to #TeamMoldova."

The Romanian national anthem was the Moldovan anthem for a brief period after the fall of the Soviet Union in the early 1990s.

The anthem mix-up is an embarrassing mistake for the ATP Cup, occurring on the first day of competition for the fledgling tournament.

Tennis fans took to Twitter to express their disappointment at the error:

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While others were more sympathetic:

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Sharing a border to Moldova's west, Romania and Moldova have a complex relationship.

Most of Moldova was part of Greater Romania between World War I and World War II, and in recent years there has been a movement to unify the two countries.

Romanian is also the official language of Moldova.

Moldova was one of the last nations to qualify for the 24-team ATP Cup.

Team Moldova posed with the Moldovan national flag before their ATP Cup tie ( Twitter: ATP Cup )

It was led in the tournament by world No.46 Radu Albot whom last year became the first player from his country to win an ATP singles title by claiming the Delray Beach Open.

Albot is Moldova's highest-ever ranked player while the country's second-highest ranked player in Sydney is world No.818 Alex Cozbinov.

Belgium went on to complete a clean sweep of their three matches against Moldova, winning the tie 3-0.

Past anthem bungles

It is not the first time officials have been left red-faced by an anthem gaffe at a major tennis tournament.

In 2017, Germany fumed when a banned verse of their national anthem dating back to the World War II era was sung during the opening ceremony for the Fed Cup quarter-final against the United States.

"I thought it was the epitome of ignorance. It is the worst thing that has ever happened to me," German Andrea Petkovic said at the time.

And before the 2003 Davis Cup final, Spain's pre-civil war republican anthem was played before their clash with Australia.

Spain's sports minister Juan Antonio Gomez-Angulo waved furiously and yelled from the stands before Australian captain John Fitzgerald was forced to apologise to the crowd afterwards.

Alexander Cozbinov of Moldova lost his match to Belgium's Steve Darcis. ( AAP: Craig Golding )

ABC/AAP