Former champion Moser-Proell, who dominated women's ski racing in the 1970s and is now 62, was in the stands to watch Vonn win the sprint downhill, run over two legs on a shortened course because of insufficient snow on the upper slopes.
Vonn clocked a combined time of two minutes 11.17 seconds, beating Canadian Larisa Yurkiw into second place. Austrian Cornelia Huetter was third, 1.66 seconds behind the American.
"I didn't let the pressure get to me and to be tied with Annemarie is incredible so I'm very happy and looking forward to tomorrow's (super-G) race," Vonn told reporters.
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Austrian Moser-Proell won her 36th downhill in January 1980, the same year she became Olympic champion in the discipline. Six-times overall World Cup champion, she also won the downhill world title twice, in 1974 and 1978.
The Zauchensee race was the first two-legged downhill in the women's World Cup since Are, Sweden, in 2002. Vonn, now 31, competed in that race as a 17-year-old and was the only skier on Saturday's start list to have raced in a sprint downhill before.
"I think the classic format is the best but it's nice to do something different," Vonn said. "It's nice to challenge yourself and there's definitely a lot more pressure when you're leading the first run."
The win put Vonn within 58 points of overall World Cup leader Lara Gut, of Switzerland, who did not finish Saturday's first run. Vonn leads the downhill standings by 50 points over Huetter.
Vonn has now won 72 World Cup races in all disciplines. Only Swede Ingemar Stenmark, who dominated the men's technical races in the late 1970s and the 1980s, has won more, with 86.
A men's World Cup giant slalom scheduled for the Swiss resort of Adelboden on Saturday was called off because of dense fog.
(Writing by Clare Fallon in London,; editing by Ed Osmond and Ian Chadband)
