Pianist Van Cliburn returned to the concert stage Monday night after an 11-year absence, receiving a standing ovation at the end of Tchaikovsky's Piano Concerto No. 1, 13 curtain calls and four encores. A crowd estimated at 10,000 to 12,000 was on hand at the Mann Music Center, an open-air amphitheater in Philadelphia, for the concert and tickets sold for up to $125. "This is a very sentimental evening for me," Cliburn told the audience before the performance. "This is an evening of remembrance of two wonderful friends." The pianist dedicated the concert to Eugene Ormandy and Fredric R. Mann. Ormandy, who died in 1985, was music director of the Philadelphia Orchestra for 44 years. Mann, a former U.S. ambassador, headed the summer concert festival at the music center from 1949 until his death in 1987. In addition to the Tchaikovsky, Cliburn performed Liszt's Piano Concerto No. 1. The Tchaikovsky was Cliburn's signature number after he won the first Tchaikovsky Competition in Moscow in 1958. He was an instant celebrity at age 23 and the first classical musician ever given a ticker-tape parade in New York. Two decades later, he began an 11-year hiatus saying his schedule of as many as 100 concerts a year was too grueling. He has given two private performances since 1978--at the White House in December 1987 during Soviet leader Mikhail Gorbachev's visit, and January 1988 at the Bob Hope Cultural Center in Palm Springs.