Twelve months ago, Pennetta was bundled out by qualifier Yulia Putintseva at the first hurdle and avoided coming a cropper against another unheralded opponent, defeating wildcard Gabriela Dabrowski, 6-4, 6-1.
"I think she's really good and I was surprised by her level in the first set," Pennetta said. "I'd played her in doubles, but never in singles, and she was moving unbelievably well. Good technique. And the serve is pretty impressive."
Dabrowski acquitted herself well early on, recovering from dropping her serve in the fifth game to peg Pennetta back. She was not level for long, though, a fizzing inside out forehand from Pennetta bringing up another break point, which the Canadian could only follow up with a limp double fault.
In the second set, the gulf in class and experience - Dabrowski was playing in just her sixth WTA main draw match - began to shine through. A couple more thumping forehands brought up three break points in the third game, Dabrowski shanking a backhand wide to hand over the advantage. After just 69 minutes, the Italian arrived at match point, punching away a backhand volley to book her date with the World No.1.
Pennetta has enjoyed plenty of success on hardcourts in recent times, winning Indian Wells and reaching the quarterfinals of the US Open last year. She will need to summon memories of these outings if she is to have any chance against Williams, from whom she has prized just one set in six previous meetings.
"It's going to be nice because I'll play one of the best players ever," Pennetta said when asked about facing Williams. "But it's good because she's the hardest test and I'll see where my game is."