The 26-year-old from Wiesbaden swam 200m in just 2 minutes, 8.58 seconds on Saturday, smashing her own German record set in 2009 by 22 hundredths of a second.
“I wasn't expecting it. I wanted to start off easy and then ramp it up,” the swimmer told Focus magazine on Saturday.
Benjamin Starke from Berlin - who won the 4x100m medley relay bronze with the German team at last year's world championships - produced the third-fastest time in the world this year in the 100m butterfly with a time of 51.95 seconds.
Although both swimmers' times came under the Olympic qualifying standard in this morning's heats, only a top-two finish in the final will confirm their places at the London games in July.
Meanwhile, world record holder Paul Biedermann drifted easily into the final in the 400m freestyle.
“I was much more relaxed than yesterday and felt much better,” the 25-year old from Halle told the paper.