Davenport returned to the tour last year after having her first child
Lindsay Davenport could not repeat her stunning third-round form as she lost to Russia's Dinara Safina in the last 16 at the Sony Ericsson Open.
The American, 31, beat world number two Ana Ivanovic on Sunday but found Safina too tough, going down 6-3 6-4.
Justine Henin, Svetlana Kuznetsova, Jelena Jankovic, Venus and Serena Williams all made the quarter-finals.
Roger Federer reached the last 16 after Robin Soderling retired trailing 6-3 3-0, but Jo-Wilfried Tsonga went out.
The 12th seed and Australian Open runner-up lost 6-3 6-3 to fellow Frenchman Julien Benneteau.
Federer was satisfied at reaching the last 16, where he will face Argentina's Jose Acasuso.
If I'm playing on cloud nine, I'm trying to get to cloud 10, and actually cloud 11
"You're sort of happy you got through to the next round," said the Swiss.
"You're not happy for your opponent, because it's never a way you want to win a match, but you've got to push him to give up."
Also through to the last 16 is sixth seed Andy Roddick, who beat Ivo Minar from the Czech Republic 7-6 6-4, while Andy Murray's conqueror Mario Ancic beat 18th seed Juan Monaco 7-6 4-6 6-1.
Elsewhere, fourth seed Nikolay Davydenko of Russia beat Italian Simone Bolelli 6-7 (5-7) 7-5 6-1.
Davenport simply could not find the form that did for Ivanovic on Sunday, making 34 unforced errors, including six double faults, and 20 winners.
"She did everything better than I did," admitted Davenport. "I came up against a player today that was real intense and real eager to win.
"That's the thing with tennis, every day you start over, but hopefully more positives than negatives come from this tournament."
The leading women flourished, with top seed Henin in good form as she saw off Elena Vesnina 6-2 6-2 to set up a clash with Serena Williams, who beat Kaia Kanepi 6-3 6-3.
It will be a rematch of last year's final, which Henin lost despite having two championship points.
"Actually it's a very good memory from last year, even if I had match points and I lost the match," said Henin, who went on to beat Williams at the French Open, Wimbledon and the US Open.
"It was a day that I understood that I could win against Serena, and that I could do it in Grand Slams three times in the same year."
Venus Williams hit 23 winners as she beat 17-year-old Dane Caroline Wozniacki 6-3 6-3 to set up a quarter-final against third seed Kuznetsova, who beat Shahar Peer 7-6 (7-4) 6-3.
"I played some good tennis and aggressive when I needed to, and a lot of really good service games," said Williams.
"I definitely feel like I'm playing well. I'm always trying to take it to another level, regardless.
"If I'm playing on cloud nine, I'm trying to get to cloud 10, and actually cloud 11."
Fourth seed Jankovic defeated Jie Zheng of China, 6-4 7-5, and next faces 10th seed Elena Dementieva, who beat Sabine Lasicki 6-3 6-2.