Monterrey - 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 quarter-finals of the Monterrey Open.
Kerber, ranked sixth in the world, broke Kudryavtseva 10 times, but dropped her own serve eight times to allow her Russian opponent to stay in the match on 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.