Alshammar clocked 58.51 seconds in the heats of the 100m individual medley, three hundredths faster than the time set by Australia's Emily Seebohm last August in Hobart.
"I have learned not to expect too much at once. So when it happens it is all the more special," Alshammar said after her record-breaking swim.
The Swedish swimmer decided to stand over the final on Saturday evening in order to focus on the butterfly, to devastating effect.
She smashed the world record in the 50 metre butterfly final, clocking 24.75 seconds, bettering the time of 24.99sec established by Marieke Guehrer of Australia in November 2008 in Berlin.
Jessica Hardy of the United States improved her own mark in the 50 metre breaststroke, touching the wall in 29.45 seconds.
She had established the previous record in Manchester in April 2008.
Her compatriot Peter Marshall then swam the men's 50m backstroke in 22.75sec, also improving the previous world record he had set in November 2008 in Berlin.
The autumn World Cup meets are the last to allow the so-called 'super suits'. The international swimming body FINA has previously advised that the suits will be banned from the turn of the year.