Top-seeded Angelique Kerber has defeated Alla Kudryavtseva 6-4, 4-6, 6-2 in a match featuring 18 breaks of serve to advance to the quarterfinals of the Monterrey Open.
The sixth-ranked Kerber broke Kudryavtseva 10 times, but dropped her own serve eight times to allow her Russian opponent to stay in the match Thursday.
Third-seeded Maria Kirilenko of Russia also advanced with a 6-0, 4-6, 6-1 win over qualifier Jovana Jaksic of Serbia.
American Lauren Davis wasted four match points and saved a set point in the second set tiebreaker before finally defeating countrywoman CoCo Vandeweghe, 6-4, 7-6 (8).
The 19-year-old Davis is ranked a career-high 71st, up from No. 319 at the start of 2012.