The Williams sisters have seldom spent such a miserable day together.

Venus Williams botched routine shots all the way through a 7-6 (2), 6-4 loss to Italy’s Flavia Pennetta on Thursday, the first major upset at the Cincinnati Open. She made 38 unforced errors, repeatedly dumping balls into the net or well beyond the baseline.

“I saw her after the match, and she just said she had made a lot of errors,” younger sister Serena said. “I was like, ‘Wow.’ I didn’t think I would do the same thing.”

Not the same. Worse. Playing on the same court a few

hours later, Serena topped her sister in confounding mistakes. She had 44 unforced errors during a 7-5, 6-4 loss to Austria’s Sybille Bammer, who reached the quarterfinals of a tournament for only the third time this year.