Perhaps it was a bad omen for the Williams sisters when one of Venus' shots from the baseline pegged Serena in the back during their doubles match.
Serena shook it off, but the match went downhill from there.
After winning the first set in their Australian Open quarterfinal against the top-ranked Italian duo of Sara Errani and Roberta Vinci, the Williams sisters lost 3-6, 7-6 (1), 7-5, halting the Americans' bid for their 14th Grand Slam doubles title.
Older sister Venus was to blame for a string of errors at crucial moments, including two double faults before losing her service game to give the Italians a 6-5 edge in the third set.
Errani served out the 2-hour, 36-minute match without dropping a point, thanks in part to Venus sending the final shot into the net.
"We don't think she played bad," Errani said about Venus at a post-match news conference. "Maybe she made some mistakes in the last few games ... but that's pressure and it's normal at that stage."
"It shows they're human," she added.