(CNN) -- After Venus Williams beat Caroline Wozniacki at the Dubai Duty Free Tennis Championships, it looked as if a first all Williams tennis final in five years was on the cards.
But someone forgot to tell Alize Cornet.
The Frenchwoman stunned a sluggish Serena Williams in the second semifinal Friday, meaning a Williams versus Williams clash for silverware -- they haven't met in a finale since the year-end championships in 2009 -- will have to wait.
It was Serena Williams' first tournament since a back injury hampered the 17-time grand slam champion at the Australian Open, and she accepted a wildcard from organizers to fend off the boredom from just practicing.
Perhaps rust was an issue. Serena Williams likened her play against Cornet in the 64 64 reverse to a 'turtle' and gave herself the harshest of grades.
"I started out extremely slow," Williams was quoted as saying by the WTA's website. "I have actually been looking at a turtle every day -- it's a really cute turtle in the hotel. Maybe I was too influenced by it. I need to play better than that if I want to be playing on the professional tour. Maybe I can go to the amateurs.
"I haven't felt good this whole week, to be honest, just from my first match.
"She played really well. I didn't play well. I tried, though. I just kept hitting errors. I don't think I've made that many errors in a match in at least three, maybe four years. I think out of a 10, I was at, like, -283, so... wow."
Cornet, France's No. 1, had lost all three of her previous encounters against Serena Williams and was 0-17 lifetime against the top four, but she served impeccably against the American.
She took advantage of Williams' normally strong second serve, winning 62 percent of those points, and did her usual scrambling from the baseline.
"It's my best ever win, but I haven't realized it yet," Cornet told reporters. "I played a very good match. I didn't even realize who I was playing and that's the way I had to be.
"I forgot it was Serena on the other side and just got on with my game."
Venus Williams has been slowed by Sjogren's Syndrome, injuries and age but the elder Williams continues to flourish in Dubai, winning her last 14 matches.
The 33-year-old owned a 4-0 record against former world No. 1 Wozniacki -- without losing a set -- prior to the semifinals and once again the Dane was overpowered, losing this time 63 62.
"I feel like I've just gotten so much better since my first round to now, feeling comfortable on the court, feeling comfortable when I'm behind, feeling comfortable when I'm in the lead," Williams was quoted as saying by the WTA's website. "It reminds me of when I first came on tour, just having to learn a lot, and I feel like I'm learning those lessons all over again.
"I had a lot of tough losses, and I realized I had to go through it. Even if I didn't necessarily get the result I wanted, I realized I was getting better.
"For me, and for every player, you just have to keep stepping up to the line and believing in yourself."
If Cornet downs Venus Williams, she would become one of the few players to beat the sisters at the same tournament. Cornet, though, trails Venus Williams 3-0 in their head-to-heads.