A bad day at the office costly for Wozniacki

Top-seeded Caroline Wozniacki chalked up her US Open semi-finals loss Friday to Russia's Vera Zvonareva as a bad day at the office - one that may have cost her the number one ranking and a million-dollar bonus.

The 20-year-old Dane, who had breezed through five straight-set wins while dropping just 17 games, fell 6-4, 6-3 in 85 minutes on a windy Arthur Ashe Stadium centre court.

"She played a really good game, definitely," Wozniacki said after her 13-match winning streak was halted. "She was not missing a lot. She was going for her shots.

"Most things were going in. I had chances, and I don't know, I made some mistakes today that I usually don't do.

"Yeah, it was a tough day for me in the office."

Wozniacki was working on a second successive trip to the Open finals after finishing runner-up in 2009 to Belgian Kim Clijsters.

A triumph at Flushing Meadows this year would have given her a first grand slam title, the world number one ranking and a $1 million bonus for winning the US Open series with her wins in Montreal and New Haven leading up to the grand slam.

"I was really trying. I was really trying to move my legs even more, trying to get into this rhythm where I could lead in this game," Wozniacki said.

"But she was really strong today and she played really well."

Wozniacki, who wins by grinding down opponents with her steady groundstrokes, was outsteadied Friday by the Russian. She made 31 unforced errors in the match, 20 of them coming from her forehand.

The Dane denied she felt tired after an arduous season in which she captured a tour-leading four titles.

"I'm actually not feeling too tired, to be honest with you," Wozniacki said. "I wouldn't have minded playing one more match."