"Skinny. Old. You discovered me too late," Julio Iglesias told an adoring and, for the moment, incredulous capacity crowd at Merriweather Post Pavilion last night. If affection could kill, Iglesias would be in sorry shape. His concert, to be repeated tonight, amounted to a love feast for his fans, many of whom had never before seen the international superstar perform.

He opened by singing a duet with himself. As his image flickered on a screen behind him, Iglesias walked out on stage singing to tumultuous applause. Soon the curtain parted, revealing 20 musicians and three vocalists perched on a sparkling white set. Throughout the show, the stage was bathed in dark colors, enhancing the romantic mood Iglesias created with his songs.

Like his big-band arrangement of "Begin the Beguine," much of what Iglesias sang was in Spanish. But there also were songs in French and English, notably "Moonlight Lady" and "As Time Goes By."

His voice, a sensuous baritone, was in fine shape throughout the evening. Even if it hadn't been, Iglesias' humor probably would have saved the day. At one point, for example, he explained how a four-letter word served as his introduction to the English language, and how it took him two months to learn to pronounce the word "girls," so that he could record "To All the Girls . . ." with Willie Nelson.

And Iglesias did sing "The Girls," also as a duet with himself. This time, however, the image of Iglesias on the screen was wearing a red bandana.