His death was reported on the Web site of the International Tennis Hall of Fame & Museum.

With a solid if not overly powerful left-handed serve, reliable groundstrokes, excellent foot speed and quick hands at the net, Larsen was the top-ranked player in the country in 1950, when he won the United States National Championship, the precursor to the United States Open, in Forest Hills, Queens, defeating Herbert Flam in a five-set final. In 1954 he lost to Tony Trabert in straight sets in the finals of the French Open. He also won U.S. Indoor, U.S. Hard Court and U.S. Clay Court titles. In 1955 he was ranked No. 3 in the country.

More than for his victories, however, Larsen was known for his personality quirks. On side changes during a match, his routine included stepping on certain lines and avoiding others. He sometimes addressed an imaginary bird on his shoulder, and he was widely known as Tappy because of his superstitious habit, perhaps a compulsion, of tapping people and things a given number of times on given days.

"Every day was a onesie day, or a fivesie day — that's what he called them — and if he happened to run into you on, say, a threesie day, he'd tap you three times," Dick Savitt, the 1951 Wimbledon champion, said in an interview this week.

Savitt also recalled that Larsen was not an ascetic athlete. A smoker, a drinker and a partygoer, he earned his success in spite of his disdain for training.

"That's the understatement of a lifetime," Savitt said. "I don't think he knew what the word 'training' was, but he was in great shape. He was thin and he could play all day."

Savitt, who lost to Larsen in the semifinals of the 1950 United States championship and beat him at Wimbledon in 1951, had a long history of playing against him, beginning with the national collegiate tournament in 1947.

"The first time I met him, he came on the court wearing long pants with his pockets bulging with cigarettes and keys and things," Savitt said. "He thought he had a lucky eagle following him; he'd always be looking behind him to see if the eagle was there. One day at Wimbledon a bird flew on the court, and it stayed there for a while, and then it started to fly off, and in the middle of a point he threw his racket at the bird."

On Nov. 10, 1956, Larsen lost control of his Italian motor scooter on a Northern California highway, an accident that sent him into a coma for three weeks, eventually cost him the sight in his left eye and left him partially paralyzed. Two months later, in a much publicized event, Savitt and other tennis players, including Don Budge, held a benefit tennis match to raise money for Larsen's medical bills. He never competed on the tennis court again.

Larsen was inducted into the Tennis Hall of Fame in 1969.

Arthur David Larsen was born in Hayward, Calif., on the east side of the San Francisco Bay, on April 17, 1925, and grew up in nearby San Leandro. According to San Leandro Bytes, a news Web site, he began playing tennis at age 11 and won a tournament at the Olympic Club in San Francisco when he was 14. After high school he fought in World War II, and the trauma of that experience is sometimes offered as an explanation for the tics and peculiarities he evinced afterward. After the war he played tennis for the University of San Francisco, which won the national championship in 1949.

Survivors include his companion, Aline Mestas, and a sister, Joyce A. Stengel.

"He was a very amusing sort of guy," Gardnar Mulloy, Larsen's former doubles partner, recalled this week. "It was easy to play jokes on him because he'd believe everything. Just point out some beautiful woman and say she said she's frantically in love with him: 'Just go up to her and ask her if she wants to make out.' A couple of times he got slapped."