Justine Henin-Hardenne and Elena Dementieva survived plucky fight-backs before reaching the last 16 at the U.S. Open on Saturday.
French Open champion Henin-Hardenne, the seventh seed, took the first nine games of her 6-0, 7-6 third round win over South Korean Cho Yoon-jeong.
Cho, though, suddenly came to life and forced a tiebreak with some punishing groundstrokes before Henin-Hardenne restored order, winning it 7-4.
"I took a step back on the court," conceded the Belgian, who was the champion at Flushing Meadows in 2003. "She took her opportunities and put me under a lot of pressure."
Henin-Hardenne plays either France's Mary Pierce, whom she thrashed in the French Open final in June, or Serbia and Montenegro's Jelena Jankovic in the last 16.
Sixth seed Dementieva, who was runner-up last year, flirted with defeat in her 6-1, 4-6, 7-6 victory over fellow Russian battler Anna Chakvetadze.
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Two alluring men's third round matches were taking place later on Saturday, with Spanish second seed Rafael Nadal facing in-form U.S. player James Blake.
That match on Arthur Ashe Court was due to be followed by the clash between 35-year-old U.S. seventh seed Andre Agassi and dangerous Czech teenager Tomas Berdych.
Chile's Olympic champion Nicolas Massu reached a grand slam fourth round for the first time when he thrashed Switzerland's Stanislas Wawrinka 6-4, 6-3, 6-0.
Women's second seed Lindsay Davenport will seek a place in the last 16 when she faces Spain's Anabel Medina Garrigues in the evening session.