ATP Cincinnati Masters second seed Novak Djokovic says he has to remind himself which continent he is on as his fast-paced schedule spins swiftly with the Olympics done and the US Open near.
"If you don't keep track of time and places where you are, it happens -- sometimes you wake up and say, 'OK, which time zone am I in right now?,'" Djokovic said.
Djokovic made the quick-change from Wimbledon Olympic grass to Toronto hardcourts last week to win Canada's Masters event.
"It's the way it is for everybody, mostly for top players," he said. "We are aware of the fact that Olympic Games are going to make our schedule more difficult and busier than previous years.
"That's what happens always in the tennis schedule when you have Olympic year coming up. We all tried to work our schedule around that. For now, I'm feeling good."
Djokovic will play his opening match on Wednesday against Italian Andreas Seppi, with top seed Roger Federer and Olympic gold medalist Andy Murray also opening then.
In Tuesday first-round matches, US 10th seed Mardy Fish ousted Spain's Feliciano Lopez 6-2, 6-3 while longtime friend and two-time tournament champion Andy Roddick lost to Frenchman Jeremy Chardy 7-6 (7/4), 6-3.
"I felt fine early on, and then I had one lunge forehand and the back kind of goes out or spasms a little bit. It got progressively worse," Roddick said.
"I feel a lot better about where my game is at now -- today was just one of those things, what are you going to do about it?"
German Tommy Haas continued his fighting return to top form by outlasting Argentine David Nalbandian 6-7 (0/7), 7-6 (7/4), 6-3 in a match lasting almost 3.5 hours.
Haas won the Halle title in June on grass over Federer and played in finals at Hamburg and Washington. He reached the quarter-finals last week in Toronto and has lined up a Cincinnati date with Olympic bronze medalist Juan Martin del Potro, the eighth seed.
Japan's 14th seed Kei Nishikori opened with a victory over Marcel Granollers 6-1, 6-2.
In women's play, unseeded Olympic doubles champion Venus Williams found herself in a struggle with Russian Maria Kirilenko, the 12th seed, before pulling out a 6-3, 6-7 (5-7), 6-2 first-round win in nearly 2 1/2 hours.
The 32-year-old American was helped by 11 aces but did not do herself any favors as she failed to serve out a straight-sets win.
"I think I 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 of 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 trailed 7-6 (10/8), 3-1.
Germany's Angelique Kerber was first into the third round, beating Timea Babos of Hungary 3-6, 6-1, 6-2.