Serena Williams began the defence of her China Open title with a straight-sets win over Spain's Silvia Soler-Espinosa in Beijing.

The world number one, who beat Jelena Jankovic to win last year's tournament, booked her place in the second round after securing a 7-5 6-2 victory over qualifier Soler-Espinosa in one hour 13 minutes.

Top seed Williams fired down nine aces and won 24 out of 32 points on her first serve at the National Tennis Center - the venue built for the 2008 Olympics tennis competitions.

Although by no means in top gear, Williams appeared to have shaken off the viral illness that forced her to retire from her second-round Wuhan Open match against Alize Cornet six days ago.

"It was really exciting to come away with the win today. I got off to a slow start, but I just really, really wanted to win and get some matches under my belt, so it was good," Williams told wtatennis.com.

"I'm really good now. I mean, every day I've been getting better, so I feel so much better now."

Ninth seed Ana Ivanovic had an even easier passage to the next round, needing just one hour 12 minutes to wrap up a 6-2 6-1 win.

The Serbian sent down five aces and won 35 of 59 points on her first serve to clinch a commanding victory.

Cornet ended 10th seed Jankovic's interest in the tournament in the longest match of the round.

Frenchwoman Cornet won the first set before her Serbian opponent hit back to take the second but the 24-year-old world number 114 kept her composure to wrap up a 7-5 3-6 6-4 victory in two hours and 39 minutes.

Joining Williams, Ivanovic and Cornet in the second round are 13th and 14th seeds Lucie Safarova and Flavia Pennetta, who defeated Camila Giorgi of Italy and American Christina McHale respectively with identical triumphs of 7-6 (7/3) 6-4.

China's Peng Shuai defeated compatriot Zhang Kai-Lin 6-4 6-1, but Zhang Shuai fell at the first hurdle with a 6-1 6-4 defeat to Frenchwoman Caroline Garcia.

Germany's Mona Barthel fought back from a set down to see off American Bethanie Mattek-Sands 4-6 6-1 6-4, while Bulgaria's Tsvetana Pironkova was a 6-4 6-1 winner over Maria Kirilenko of Russia.

American Lauren Davis breezed into the second round thanks to a 6-3 6-3 win over China's Xu Yi-Fan.

In the men's competition, fourth seed Marin Cilic saw off home favourite Yan Bai 6-3 6-4 to set up a second-round encounter with Portugal's Joao Sousa, who defeated Teymuraz Gabashvili of Russia 1-6 7-6 (7/4) 6-4.

Fifth seed Grigor Dimitrov was made to work to secure safe progress to the second round, the Bulgarian recovering from a mid-match wobble to win 6-1 3-6 6-3.

Viktor Troicki was a 6-3 6-4 winner over Mikhail Youzhny, while Vasek Pospisil secured a 6-4 6-3 triumph over Lukas Rosol.