Argentinian veteran David Nalbandian defeated Japan's Kei Nishikori 6-4, 6-4 on Monday to book a second-round clash with world No. 4 Andy Murray at the ATP Cincinnati Masters.
As this hardcourt US Open tuneup for both men and women gathered steam, Argentina's Juan Ignacio Chela and American Ryan Harrison were battling for the dubious distinction of a second-round meeting with world number one and men's top seed Novak Djokovic.
The Serbian extended his lead atop the rankings released on Monday after his victory in the Montreal Masters on Sunday -- a victory that gave him his ninth title of 2011 and made him the first man to win five elite Masters titles in the same season.
Djokovic and the rest of the top eight men's seeds have first-round byes, as do the top eight women, who are led by world No. 1 Caroline Wozniacki of Denmark.
In early WTA action, Russian Ekaterina Makarova set up a second-round meeting with second-seeded compatriot Vera Zvonareva with a 7-5, 6-3 victory over Spain's Maria Jose Martinez Sanchez.
Israel's Shahar Peer defeated Wimbledon semi-finalist Sabine Lisicki of Germany 6-4, 7-6 (7/4) to set up a second-round clash with third-seeded Victora Azarenka of Belarus.
Australian qualifier Anastasia Rodionova, ranked 139th in the world, crushed 42nd-ranked Polona Hercog 6-0, 6-0 to set up a meeting with fourth-seeded Maria Sharapova.
Russian Svetlana Kuznetsova, seeded 14th and trying to bounce back after a first round exit in Toronto last week, defeated US qualifier Jill Craybas 6-3, 6-4.
Monday night's action featured American Andy Roddick, the men's 11th seed, and former French Open champion Ana Ivanovic, the women's 15th seed.
Roddick, who won singles titles in Cincinnati in 2003 and 2006, will face Philipp Kohlschreiber of Germany.
Roddick is coming back from an abdominal injury suffered in practice in July and hasn't played since a third-round defeat at Wimbledon.
Ivanovic, a semi-finalist here last year, takes on American Alexa Glatch.
In other early matches, unseeded Italian Fabio Fognini upset 14th-seeded Viktor Troicki 6-4, 6-1, the 38th-ranked Fognini's first victory over the 16th-ranked Serbian in three attempts.
Bulgarian wild card Grigor Dimitrov advanced to a second-round clash with fifth-seeded David Ferrer of Spain with a 6-3, 7-5 victory over Turkish qualifier Marsel Ilhan.