ESPN Tennis

BEIJING -- Andy Roddick eased past Juan Carlos Ferrero to make the semifinals of the China Open on Friday, as a pair of unheralded challengers sent seeded opponents packing.

After struggling with his serve early, the former U.S. Open champion smashed his racket in frustration on the way to losing the first set 2-6.

"That racket didn't want to be here any more, so I let it out ... I was pretty upset and pretty fed up with the way I was playing," Roddick said afterwards.

The release seemed to help, however, as the 26-year-old quickly found his groove in the second set, eventually finishing with 23 aces in the 2-6, 6-3, 6-4 win over the unseeded Spaniard.

Roddick remains in the hunt for one of four remaining places for November's Tennis Masters Cup in Shanghai, which groups the year's eight top-performing players.

Swiss Roger Federer, Spaniard Rafael Nadal, Briton Andy Murray and Novak Djokovic of Serbia have already qualified.

In other men's action Friday, Dudi Sela upset No. 6 Tommy Robredo 6-4, 6-1 to reach his first semifinal in a major ATP event. Sela was boosted by two wins over the weekend in a Davis Cup tie against Peru.

Sela trailed early against Robredo, but turned things by attacking and hitting to the Spaniard's backhand.

"Every short ball he hit, I didn't wait," said Sela, who upset No. 1 David Ferrer on Thursday. "I went for the ball. I knew I had to attack him. If not he's going to move me around."

Two other seeded players also lost on Friday.

No. 7 Rainer Schuettler ousted No. 4 Richard Gasquet 4-6, 6-3, 6-4, while unseeded Bjorn Phau upset third-seeded defending champion Fernando Gonzalez 6-3, 4-6, 6-3.

In women's action, Ana Ivanovic was ousted by local favorite Zheng Jie 7-6 (4), 2-6, 6-4.

Ivanovic, the French Open champion and former top-ranked player, was erratic with her serve and ground strokes. She led in the first set, but failed twice to serve it out before Zheng won in the tiebreaker.

In the three other quarterfinals, Jelena Jankovic defeated Daniela Hantuchova 7-5, 6-1; Svetlana Kuznetsova defeated Dominika Cibulkova 6-2, 6-4 and Vera Zvonareva stopped Anabel Medina Garrigues 6-0, 6-1.

In the semifinals, Zheng plays Kuznetsova, while Jankovic plays Zvonareva.

Wimbledon semifinalist Zheng had the support of home fans at the Beijing Tennis Center. She is the only Chinese woman still playing in the tournament after four others lost in the first round.

Zheng previously beat Ivanovic en route to the Wimbledon semifinals.

"This is a good win for me," she said. "It was in China and in front of my home crowd. There were lots of fans supporting me, which gave me even more motivation."

The 30th-ranked Zheng is hoping the ranking points earned will push her past her previous career high of No. 27.

Ivanovic has battled hand and leg injuries since winning in Paris, which has limited her play and confidence. However, she described her match Friday as "one of the best" since the French Open.

"I haven't had many matches in the last three months," she said. "Since the French Open, you can count them on one hand the number of matches I played.

"I've been really struggling with injuries and it was a very frustrating time. But now I am confident again that I play 100 percent -- and I can go on the court and work 100 percent."

Reuters and The Associated Press contributed to this report.