The 1994 champion was not bothered by the rain

A lengthy rainbreak interrupted the match in the third game and 1994 champion Martinez grabbed a 4-1 lead when play resumed on court 13.

The 23-year-old Osterloh saved one set point on her own serve in the eighth game but Martinez, given another opportunity, hit a forehand winner into the corner to take the set.

The 19th-seeded Spaniard had to save a break point in the fifth game of the second set, with another winning forehand.

That served as a wake-up call for the Spaniard, who changed her tactics and rushed to 40-0 in the following game and made the break when her opponent served a double-fault.

Osterloh, ranked 51st in the world, saved three match points at 5-2 and one more at 5-3 but Martinez converted the fifth with a backhand winner.

The 29-year-old Martinez, who has dropped to 20th in the world from a career high of two in the mid 1990s, now plays Lina Krasnoroutskaya.

The Russian teenager beat Barbara Schwartz of Austria 6-3 6-4.

Russian Krasnoroutskaya plays Martinez next

The unseeded 17-year-old Krasnoroutskaya, who reached the quarter-finals at the French Open this year, broke in Schwartz's first two service games.

Before she could take advantage, the rain fell, but she converted her opportunities when play restarted.

Schwartz battled gamely but without profit as Krasnoroutskaya ran her around court 18 with searing groundstrokes in the second set.

Twelfth seed Magdelena Maleeva achieved her best Wimbledon performance when she outhit American Amy Frazier 6-3 6-2.

Frazier's serve was not powerful enough to trouble the Bulgarian 26-year-old who was also a better exponent of the baseline chess the two played on court three.

Maleeva has reached the fourth round of a Grand Slam eight times but never at Wimbledon.