Cincinnati - German Tommy Haas continued his fighting return to top form which has erupted in the last few months, with the 34-year-old outlasting Argentine David Nalbandian 6-7 (0/7), 7-6 (7/4), 6-3 in a marathon lasting almost three-and-a-half hours at the ATP-WTA Cincinnati Masters.
Haas won the Halle title in June on grass over Roger Federer and played finals in Hamburg and Washington. He reached the quarter-finals last week in Toronto at the Masters 1000 and has lined up a Cincinnati date with Olympic bronze medallist Juan Martin del Potro, the eighth seed.
Japan's 14th seed Kei Nishikori opened with a victory over Marcel Granollers 6-1, 6-2.
Meanwhile, on the women's side Wimbledon winner Petra Kvitova remains committed to joining the women's elite with the quiet Czech hoping to follow up Monday's title in Canada here as well.
The fourth seed arrived early on Tuesday after beating 2011 French Open winner Li Na Of China in a battle of former Grand Slam champions to claim the crown in Montreal, her first title of the season.
After a bye, Kvitova will open against German Mona Barthel, who already has a match under her belt from the first round.
Kvitova looks upon this final major tune-up prior to the start of the US open as a chance to keep up the improvement on North American hardcourts.
"I need to be positive. In the past I didn't have a great result here," said the 22-year-old. "Finally I have won (a title). I hope that it will be continuing in this pre-US Open period and in the US Open."
Kvitova, who had been bothered by breathing difficulties, said her allergies were fine in the chill of Montreal and that she is now hoping for the best in what should be American Midwest summer heat.
"Here it's more humid, so I will see how it goes," she said. "I'll try my best and try to fight not only with the opponent, but with my asthma also."
On court, unseeded Olympic doubles champion Venus Williams found herself in a struggle with Russian Maria Kirilenko, the 12th seed, before taking a 6-3, 6-7 (5/7), 6-2 first-round victory after nearly two and a half hours.
The 32-year-old American was helped by 11 aces but failed to serve out a straight-sets win.
"I think was putting too much emphasis on my serve," Williams said. "I wanted to win it off the serve and then when I had to hit some groundstrokes I just wasn't patient enough.
"I should have stuck in there and worked the point and hit a lot balls and be ready to win the point. I got a little impatient and that doesn't work, especially against a player like her. I changed my ways in the third."
Russian Elena Makarova eliminated Nadia Petrova when her 15th-seeded compatriot retired trailing 7-6 (10/8), 3-1.Results from the second day of the ATP and WTA Cincinnati Masters Series event on Tuesday (x denotes seeding):
Angelique Kerber (GER x5) bt Timea Babos (HUN) 3-6, 6-1, 6-2
Serena Williams (USA x2) bt Eleni Daniilidou (GRE) 6-3, 6-4
Johanna Larsson (SWE) bt Marion Bartoli (FRA x8) 6-4, 6-2
Samantha Stosur (AUS x3) bt Anabel Medina Garrigues (ESP) 6-3, 6-7 (6/8), 6-4
Sloane Stephens (USA) bt Tsvetana Pironkova (BUL) 6-4, 6-1
Anna Tatishvili (GEO) bt Klara Zakopalova (CZE) 7-6 (7/5), 7-5
Venus Williams (USA) bt Maria Kirilenko (RUS x12) 6-3, 6-7 (5/7), 6-2
Andrea Hlavackova (CZE) bt Bethanie Mattek-Sands (USA) 6-3, 7-5
Sofia Arvidsson (SWE) bt Tamira Paszek (AUT) 6-1, 2-1 retired
Sesil Karatantcheva (KAZ) bt Kiki Bertens (NED) 6-2, 6-1
Elena Makarova (RUS) bt Nadia Petrova (RUS x15) 7-6 (10/8), 3-1, retired
Sorona Cirstea (ROM) bt Yvonne Wickmayer (BEL) 6-7 (2/7), 6-2, 6-3
Daniela Hantuchova (SVK) bt Zheng Jie (CHN) 2-6, 7-6 (7/1), 6-3
Roberta Vinci (ITA) bt Madison Keys (USA) 6-3, 6-3
Anastasia Pavlyuchenkova (RUS) bt Carla Suarez Navarro (ESP) 6-4, 6-0
Yaraslava Shvedova (KAZ) bt Lucie Safarova (CZE x16) 6-3, 6-4
Chanelle Scheepers (RSA) bt Christina Mchale (USA) 3-6, 6-3, 3-0, retired
Bernard Tomic (AUS) bt Brian Baker (USA) 6-4, 6-3
Tomas Berdych (CZE x5) bt Yu Yen-hsun (TPE) 6-3, 6-4
Alex Bogomolov (RUS) bt Jarkko Nieminen (FIN) 6-4, 6-3
Kei Nishikori (JPN x14) bt Marcel Granollers (ESP) 6-1, 6-2
Tommy Haas (GER) bt David Nalbandian (ARG) 6-7 (0/7), 7-6 (7/4), 6-3
Jeremy Chardy (FRA) bt Andy Roddick (USA x16) 7-6 (7/4), 6-3
Mardy Fish (USA x10) bt Feliciano Lopez (ESP) 6-2, 6-3
Carlos Berlocq (ARG) bt Santiago Giraldo (COL) 7-5, 6-3
Sam Querrey (USA) bt Jurgen Melzer (AUT) 4-6, 6-2, 6-4
Radek Stepanek (CZE) bt Albert Ramos (ESP) 6-2, 6-2
Marcos Baghdatis (CYP) bt Alejandro Falla (COL) 6-4, 6-3
Milos Raonic (CAN) bt Richard Gasquet (FRA) 7-6 (7/4), 6-3