Wozniacki faced frequent trouble on her serve and was broken three times by the diminutive American during the one-hour, 36-minute clash on Arthur Ashe Stadium.
King, ranked 103 in the world, broke Wozniacki’s serve in the opening game of the match but midway through the set she began to spray the ball around and her game unraveled.
The 22-year-old King rallied from 2-5 to 4-5 in the second set but then lost her serve to end the match.
In the round of 16 Wozniacki will face either 15th seeded Russian Svetlana Kuznetsova, the 2004 champion, or Akgul Amanmuradova of Uzbekistan.
Czech ninth seed Berdych became the 17th player to quit the US Open through injury or illness when he retired from his third round match against Serbia’s Janko Tipsarevic.
Berdych was suffering from a right shoulder injury and needed treatment at the end of the first set, which he lost 6-4, and then called it quits when he was down 5-0 in the second.
The 25-year-old said he first felt the injury in his Cincinnati Masters quarterfinal win over Roger Federer two weeks ago before it caused him to quit his semifinal against Novak Djokovic.
“I already knew there was a problem. I had it in Cincinnati, so it was a case of just trying,” he said.
Tipsarevic will be playing in his first US Open fourth round where he will tackle either former world No. 1 Juan Carlos Ferrero or Marcel Granollers.
“I was happy to win the first set because I don’t think it had anything to do with the injury. Then I raised my game. I didn’t want to ease off and allow him back into the match,” said Tipsarevic, who has now won all four of his meetings with Berdych.
On Friday, Maria Sharapova was knocked out of the tournament in a shock third round loss to Flavia Pennetta, while Andy Murray was lucky to survive after being pushed to five sets by Robin Haase.
Sharapova was beaten 6-3, 3-6, 6-4 in the biggest upset of the tournament so far before Murray clawed his way back to defeat Haase 6-7, 2-6, 6-2, 6-0 6-4 in the second round and avoid another early exit at the last grand slam of the year.
“You’re relieved to get through a long one like that, especially when you’re behind,” fourth seed Murray told reporters.
“I’m just glad I’m in the next round and get a chance to improve and play better and give myself a chance,” added the Briton.
Defending champion Rafa Nadal strolled through to the third round when his opponent, Frenchman Nicolas Mahut, retired in the first game of the third set complaining of a stomach muscle strain with the Spaniard well in control, leading 6-2 6-2.
Sharapova, who won the US Open in 2006 but has not won a grand slam title since the 2008 Australian Open, became the biggest casualty of a tournament that has mostly gone according to the script.
The Russian third seed was one of the favorites to win the crown after winning a lead-up event in Cincinnati but made a whopping 60 unforced errors and served 12 double faults, including two in the final game.
“It’s disappointing to lose in New York. Losing isn’t fun for anyone because we work to win,” she said. “We don’t work to try to lose. So when we’re faced with a position where we can win and we didn’t in the end, it’s tough.”
For Pennetta, a quarterfinalist at Flushing Meadows in 2008 and 2009 who is seeded 26th, it was a moment to savour as she celebrated her victory on a baking hot day at the Arthur Ashe Stadium.
“I think this one is one of the best victories in my career, and is gonna be like this forever,” the Italian said.
“It’s a good moment. I’m really happy right now but it’s just a match. It’s over, and I have to be focused for the next one.”
Pennetta’s next opponent is China’s Peng Shuai, the 13th seed, who advanced with a 6-4 7-6 win over Julia Goerges of Germany in an increasingly wide open women’s draw.
None of the remaining players in the bottom half of the draw have won a Grand Slam title and the only two to have played in a final are last year’s runner-up, Vera Zvonareva of Russia, and Australia’s Sam Stosur.
Zvonareva, seeded second, beat Anabel Medina Garrigues 6-4 7-5 Friday while ninth seed Stosur, a finalist at the French Open last year, outfought Russian Nadia Petrova 7-6 6-7 7-5.
Stosur came back from a break down in the third set after squandering two match points in the second set.
Murray, who also won in Cincinnati, was in danger of bowing out after his Dutch opponent won a first set tiebreaker and took the next set to establish control.
But the Scotsman, who has played in three grand slam finals but is yet to win a major, assumed control, winning the next two sets and opening up a 4-0 lead in the fifth.
Haase, who needed treatment to his back, fought back to level the final set at 4-4 before Murray broke his serve then held to seal victory.
Murray will face Spaniard Feliciano Lopez in the third round and remains on course for a semifinal showdown with Nadal, who has been struggling for form but could not have asked for an easier day as Mahut became the 14th player this week to retire or withdraw from their match.
Former champion Juan Martin Del Potro sailed through with a 6-2, 6-1, 7-5 win over his fellow Argentine Diego Junqueira.
American Andy Roddick, the 2003 winner, silenced talk about a passing of the torch by dismissing 18-year-old compatriot Jack Sock 6-3, 6-3, 6-4, while big-serving John Isner won his all-American match against Robby Ginepri 6-4, 6-3, 6-4.
