Elena Baltacha is out of the Sony Ericsson Open after suffering a 6-1 6-3 second round loss to Belgium's Yanina Wickmayer in Miami.
The British number one, who is up to a career-high 62nd in the world rankings, was brushed aside in the opening set.
The 26-year-old offered more resistance in the second, saving six break points against the world number 14.
Meanwhile, Venus Williams and Svetlana Kuznetsova progressed safely, winning in two and three sets respectively.
Baltacha, reflecting on her loss to Wickmayer, told BBC Sport: "She played an unbelievable match, but I must take the positives from my last two events.
"I qualified for both and had my first win over a top 10 player two weeks ago at Indian Wells, so my whole season is getting better and better."
Baltacha also revealed that she was on the verge of quitting tennis before hooking up with her coach Nino Severino in 2008.
"For nine years I felt like I was banging my head against a brick wall and 18 months ago I was one week away from retiring.
"But I managed to find Nino in Ipswich and luckily for me he persuaded me to carry on.
"I was very talented and I had to see that and fight for what I had and thanks to him I did that.
"It's great playing a lot of the top players and the most important thing has been putting myself in that position and learning from it.
"It hasn't been comfortable and I've taken a few punches, but I beat a top 10 player, so I'm learning quickly."
Wickmayer, a semi-finalist at last year's US Open, will play Croat Petra Martic for a place in the last 16.
Martic booked her place in the next round with a 7-5 5-7 6-4 win over France's Aravane Rezai.
Three-time Miami winner Venus Williams defeated Romanian Sorana Cirstea 6-4 6-3 and joins top seed Kuznetsova of Russia - who beat China's Peng Shuai 6-2 3-6 6-4 - in the third round.
China's eighth-seeded Li Na was beaten 6-4 4-6 by Switzerland's Timea Bacsinszky, while Andrea Petkovic of Germany knocked out 10th seed Flavia Pennetta of Italy 6-3 3-6 6-0.
Former world number one Ana Ivanovic progressed at the expense of France's Pauline Parmentier, while Marion Bartoli and Agnieszka Radwanska also booked their places in round three.
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