Seiji Ozawa called in sick Wednesday on the opening night of his 25th season as director of the Boston Symphony Orchestra. His understudy Robert Shaw stepped in.

Ozawa, 63, is the longest-serving music director of any major orchestra. He had just returned from Russia and was set to open the season with a performance of Beethoven's Ninth Symphony.Symphony spokeswoman Bernadette Horgan said she expects Ozawa, who had a virus and was running a fever of 103 degrees, to recover in time for a performance Sunday on Boston Common.