Serena Williams returned to the top of the world with a routine win at the China Open on Tuesday but Andy Roddick and Jelena Jankovic plumbed the depths when their title defences ended in their opening matches.
Serena's 6-3, 6-2 second-round victory over Russian Ekaterina Makarova means she will replace Dinara Safina as world number one when the rankings are issued next week, ending the Russian's controversial 25-week reign.
Her fellow American Roddick, however, was humbled 6-2, 6-4 by Polish qualifier Lukasz Kubot, while Serbian Jankovic, nursing the wrist injury that forced her to retire from last week's Pan Pacific Open final, lost 4-6, 7-5, 6-2 to China's Peng Shuai.
World number two Rafael Nadal came through a thorough, 130-minute test of his fitness after a two-week layoff with an abdominal injury, beating Cypriot Marcos Baghdatis 6-4, 3-6, 6-4 in an entertaining first-round encounter.
Safina's defeat to 226th-ranked wildcard Zhang Shuai on Monday had left the way open for Williams to return to the number one spot and she never looked like blowing her chance.
The second seed was broken in her first service game and made a meal of her last but converted her fourth match point to seal the victory, raising a single finger in the air in celebration of her return to the top.
"I'm really excited," said the 28-year-old.
"Obviously I'm happy to be there because I've worked so hard this year to get there. I think I've earned it."
Men's third seed Roddick never really came to terms with Kubot's serve and the Pole's fifth ace of the match ended the world number six's reign as China Open champion.
I'm going to be making obvious statements here but I didn't play well," a clearly fatigued Roddick said.
"I was just trying stuff out there and nothing seemed to be working that well."
Nadal was playing his first match since his U.S. Open semi-final defeat by Juan Martin del Potro and was pleased with how he finished the tight contest against his fellow former China Open champion Baghdatis.
"I didn't play my best tennis, but I'm very happy with how I played in the last four games, very aggressive with the forehand and going to the net," said the Spaniard.
"My body is okay today, and tomorrow, I hope," he added.
Jankovic, seeded eighth, served for the match in the second set against Peng but her heavily strapped arm could not take the strain when the twice China Open semi-finalist forced a third set.
"It was very difficult and I couldn't really play my best tennis," said Jankovic.
"Despite that I had a chance to win in two sets but she took it to a third and my arm just didn't hold up. It's very disappointing," she added.
Maria Sharapova, who was handed her first title since her return from injury when Jankovic withdrew in Tokyo last Saturday, mounted a sensational fight back from 5-2 down in the third set to beat ninth seed Victoria Azarenka 6-3, 6-7, 7-5.
"The match isn't over until we shake hands," said the Russian. "I realised that I didn't want to be going home. I just went forward and I kept being aggressive and stayed positive and that gets you a long way."
Her fourth seeded compatriot Elena Dementieva, who won Olympic gold here last year, beat Hungarian Melinda Czink 6-4 6-3 to set up a last-16 tie against China's number one Li Na.
Fourth seed Nikolay Davydenko beat fellow Russian Igor Kunitsyn 6-1 6-7 6-2, Spain's fifth seed Fernando Verdasco beat American Robby Ginepri 6-7 6-1 6-2 and seventh seed Fernando Gonzalez also progressed with a 7-5 6-4 win over David Ferrer in the men's first round.
