Serena Williams has continued to build on her nearly flawless season at the German Open.
The fifth-seeded American opened play at the red clay event with a convincing 6-2 6-3 win over Italy's Francesca Schiavone in one of three second-round matches.
Australian Casey Dellacqua was easily ousted by Victoria Azarenka of Belarus 6-2 6-2.
Williams has won 16 straight matches, including consecutive crowns in Bangalore, Miami and Charleston.
Her only defeat in 21 matches this season came against Jelena Jankovic in the Australian Open quarter-finals. The 26-year-old exacted a measure of revenge when she beat Jankovic in the Miami final.
During her streak, Williams also has posted impressive wins against third-ranked Maria Sharapova and world No.1 Justine Henin, who was run off the court in a 6-2 6-0 quarter-final loss in Miami.
The sixth-ranked Williams and Henin will renew their rivalry if both move through to the quarter-finals this week.
The pair played for the German title in 2002, when Henin captured the first of three championships (2003, 2005).
One of the top eight seeds to receive a first-round bye, this is Williams' first appearance here since that loss.
In other second-round action, seventh-seeded Elena Dementieva of Russia hammered Ukrainian Kateryna Bondarenko, 6-1 6-2, and eighth-seeded Frenchwoman Marion Bartoli advanced with a 6-0 6-3 win against Lucie Safarova of the Czech Republic.
The first round was completed on Tuesday with 10 matches.
Vera Dushevina of Russia posted one of two upsets with a 6-2 6-3 win over No.9 seed Patty Schnyder of Switzerland.
Argentina's Gisela Dulko, fresh off a title win in Morocco at the weekend, turned in the other surprise when she rallied for a 4-6 6-1 6-2 triumph against 12th-seeded Nicole Vaidisova.
Peng Shuai of China advanced to set up a second-round match with fourth-seeded Jankovic and Akgul Amanmuradova of Uzbekistan moved through to book a match with second-seeded Ana Ivanovic, the defending champion.
Amanmuradova was playing in place of former world No.1 Amelie Mauresmo, who dropped out on Monday with a ribcage injury.
Second Round Results of the WTA German Open, Berlin
5-Serena Williams (USA) def. Francesca Schiavone (Italy) 6-2 6-3
7-Elena Dementieva (Russia) def. Kateryna Bondarenko (Ukraine) 6-1 6-2
8-Marion Bartoli (France) def. Lucie Safarova (Czech Republic) 6-0 6-3
Vera Dushevina (Russia) def. 9-Patty Schnyder (SUI) 6-2 6-3
Gisela Dulko (Argentina) def. 12-Nicole Vaidisova (Czech Republic) 4-6 6-1 6-2
Victoria Azarenka (Belarus) def. Casey Dellacqua (Australia) 6-2 6-2
Maria Kirilenko (Russia) def. Elena Vesnina (Russia) 2-6 7-5 6-2
Anabel Medina Garrigues (Spain) def. Tathiana Garbin (Italy) 3-6 7-5 2-2 Garbin retired with left thigh strain
Yan Zi (China) def. Martina Müller (Germany) 6-2 6-3
Peng Shuai (China) def. Jill Craybas (USA) 7-6 (7-4) 5-7 6-0
Alisa Kleybanova (Russia) def. Olga Govortsova (Belarus) 6-0 6-0
Catalina Castaño (Columbia) def. Galina Voskoboeva (Russia) 6-2 6-2
Akgul Amanmuradova (Uzbekistan) def. Aravane Rezai (France) 7-5 7-5