Peng Shuai
Peng Shuai of China celebrates after defeating Agnieszka Radwanska of Poland during their match at the 2014 US Open.Reuters

Even in the absence of Li Na, Chinese fans had a reason to rejoice after Peng Shuai stunned fourth seed Agnieszka Radwanska at the US Open on Wednesday.

Shuai, ranked 39 in world, ousted Radwanska 6-3, 6-4 to advance to the next round. This is her fourth career victory over a top five player and first at a Grand Slam.

The Tianjin native took her revenge against the Pole, after Radwanska had beaten her in the fourth round of the 2011 Australian Open.

"I have learned a lot from Li," said Shuai about her fellow countrywoman and world no. 3, who is missing the year's last Grand Slam due to a knee injury.

"She is one of the best players in the world. Now I will try to keep going. There is still a lot of work to do but I want to keep enjoying my tennis."

However, Shuai has achieved something that even two-time Grand Slam winner, Li Na, could not accomplish. In February, Shuai became the first Chinese player to reach number one in the world after she topped the doubles charts with Taiwan partner Hsieh Su-Wei.

Shuai, who sealed the victory on her third match point said: "Radwanska is a tough player. I had to do a lot of running, but I fought. I wanted to make it this time. I had two match points against her in 2011 in Australia and lost. This is just amazing."

Meanwhile, Maria Sharapova was made to work hard, before evntually prevailing over 95th-ranked Alexandra Dulgheru of Romania 4-6, 6-3, 6-2 at the Arthur Ashe Stadium.

It was a tough battle for the five-time champion as her serve and groundstrokes were not finding its mark. The Russian overcame nine double-faults and 46 unforced errors to win the battle on a hot and windy day at US Open.

"As tricky as it is, you have to expect not to play your best tennis and find a way to win," Sharapova said. "Overall I felt like in the end I was in much better shape than she was, and I could have played another few sets.

"Mentally that helped me a lot."

Dulgheru also acknowledged Sharapova's mental strength as a key factor in her win.

"The thing is that she's smacking the ball and she's a fighter. It can seem that she's down, that she's tired, but she's there," Dulgheru said. "She can get mentally really tough. She hangs in there with you until the end."

Sharapova will face 2013 Wimbledon runner-up Sabine Lisicki in the next round.

Venus Williams also advanced to the third round of the US Open for the first time since 2010.

The 34-year-old, who is the oldest woman left in the tournament, had an easy 6-1, 6-4 win over 78th-ranked Timea Bacsinszky of Switzerland.

"Well, now I'm happy. I won a match again. Finally I did something I couldn't do the last couple years," Williams said. "That's good stuff."

Williams saved all four break points she faced during the match and didn't create too many unforced errors. The American will now have to get past world no. 14 Sara Errani of Italy to reach the fourth round.