By Amy Tennery
NEW YORK (Reuters) - The U.S. Open marked its 50th year on Monday with a ceremony honouring the tournament's past heroes and capped by a futuristic performance by pop star Kelly Clarkson.
With Serena Williams poised for her opening match at Arthur Ashe stadium, United States Tennis Association boss Katrina Adams took the centre court stage to the late Aretha Franklin's "Respect," before inviting past tennis greats to join her.
The ceremony focussed on the social revolution of 1968, when the tournament entered the professional era and Ashe became the first African-American man to claim a Grand Slam title.
The great Billie Jean King, 1968 women's winner Virginia Wade and Tom Okker, who lost to Ashe in the men's final, joined Adams on stage in a landmark year for a tournament which started its open era at a private club in Forest Hills.
On Monday, players made their first hits inside the new Louis Armstrong Stadium, part of the sprawling Billie Jean King National Tennis Center's $600 million renovation.
The tournament got off to an explosive start with world number one Simona Halep knocked out in a stunning first round defeat.
Clarkson, wearing a silver-spangled dress, kicked off her performance with hit single "Walk Away" amid sparkling square sculptures.
She performed a few more songs but left few in doubt who the night's real star was, shouting mid-set: "I love opening for Serena Williams!"
(Reporting by Amy Tennery; Editing by Ian Ransom)