Roger Federer celebrated reaching a 22nd consecutive grand slam semi-final whilst Caroline Wozniacki ended American sensation Melanie Oudin's fine run.

Federer was made to work for his victory by 12th seed Robin Soderling but finally came through in four sets to continue his unbeaten streak against the Swede and march into a Flushing Meadows semi-final against fourth seed Novak Djokovic.

Five-time defending champion Federer had taken an 11-0 career record over 12th seed Soderling into this night match, their most recent two meetings coming at Wimbledon and in the French Open final.

The world number one made it a round dozen in victories over the Swede, reaching the last four after extending his unbeaten run at Flushing Meadows to 39 matches, Djokovic having earlier beaten 10th seed Fernando Verdasco.

It was not achieved without a fight, however, Soderling looking down and out after two one-sided sets but then making Federer work for the 6-0 6-3 6-7 (6-8 ) 7-6 (8-6) victory in two hours 33 minutes.

"This feels great," Federer said. "It was so close towards the end and it's just a great relief to come through because Robin just got better and better as the match went on.

"I knew it was going to be tough but the beginning was a bit too easy and all of a sudden he found his way into the match and showed what a great player he really is."

Federer could not account for the way the match had shifted away for him having taken a two-set lead in just 59 minutes with some crisp, clean-hitting tennis.

"I don't know, I had a really good start, it was cold so I felt at home being from Switzerland but then it got even cooler and him being from Sweden I think that played in his favour," Federer joked.

"I thought it was a great match towards the end. I got off to a flier but I'm happy I still got through in the fourth."

Of stretching his record of consecutive grand slam semi-final appearances, Federer added: "It's not (a record) I aimed for, that's for sure but it's probably one of the greatest records for me in my personal career.

"I'm just happy it keeps on going. I'm healthy and I guess that's most important because that's what has allowed me to play well at majors and I'm in for a shot again to defend my title so that's fantastic."

Of his forthcoming meeting with Djokovic on Saturday, the third year in a row they have met at Flushing Meadows, Federer said: "We've played each other the last two years, semis last year, finals the year before and we've seen what a great player he is on hard courts.

"I'm sure it's going to be a tough match, I'm looking forward to it."

Djokovic was delighted to have reached the US Open semi-finals for the third year in a row, particularly as it was his first grand slam semi of 2009.

The fourth seed from Serbia beat his Spanish rival 7-6 (7-2) 1-6 7-5 6-2 on Ashe during the day session and will play Federer for the third year in a row at the final grand slam of the season.

Djokovic had reached his first grand slam final in 2007 before going down in straight sets to Federer, while the pair met in last year's semi-finals in New York, with the Swiss star needing four sets to beat the young pretender.

"It feels great," Djokovic said of his achievement. "I haven't done that in the past three grand slams this year, so mentally it was very important for me to overcome today's challenge and to be able to win quarter-finals and to get to the semi-finals for the first time in the grand slams in 2009."

Speaking before the Federer-Soderling match, Djokovic spoke about the possibility of facing the world number one again on Saturday.

"If I play with Roger, we don't need to talk a lot about him: his records in the US Open, we all know his style of the game.

"I have been playing against him many, many times and a lot of different kind of surfaces. There are no secrets in each other's game, so it's a matter of having a good day.

"I hope I can have a good day and concentrate, and physically I'm going to have enough time to recover and be ready."

In the women's singles, Caroline Wozniacki brought fellow teenager Melanie Oudin's giant-killing run to an end under the lights at Arthur Ashe Stadium.

American 17-year-old Oudin, ranked 70th in the world, had grabbed all the headlines in the women's singles over the previous nine days as she upset a series of Russian seeds en route to the quarter-finals.

Yet having knocked out No.4 Elena Dementieva, former champion and 29th seed Maria Sharapova and 13th seed Nadia Petrova in come-from-behind three-setters, Oudin finally met her match as 19-year-old Danish ninth seed Wozniacki, also playing her first grand slam quarter-final, defeated her in straight sets 6-2 6-2.

Wozniacki's win sets up a semi-final clash with another unseeded teenager, world number 50 Yanina Wickmayer of Belgium, a 7-5 6-4 winner over Kateryna Bondarenko of the Ukraine.

"Today was a really tough match," Wozniacki said. "Melanie had such a great run and she played an amazing tournament so I'm just going to enjoy this match.

"The next match I have nothing to lose. I mean, I'm in the semi-final of a grand slam."

Oudin was also in a positive mood following her exit.

"I can take a lot from this," Oudin said. "I've had a great run here but Caroline had a great match today. I hope to come back next year and do even better."

The American had begun poorly in her first night match in a still filling Ashe Stadium, losing serve in the second game and going 3-0 down, then again in the sixth game as Wozniacki took a 5-1 lead.

An otherwise flat performance was lifted in the next game as Oudin showed some of the fighting spirit which had overcome her Russian foes in previous rounds to break back as the Dane surrendered on a double fault.

Wozniacki simply broke again and grabbed the opening set in the next game.

Another fightback from Oudin looked on the cards when she earned a double break point in the third game of the second set but Wozniacki saved them both and rode her lock to take the game via a net-cord as the ball plopped over the net into Oudin's court.

Oudin's next chance came in the fifth game when she twice won break points and twice saved game points, Wozniacki double faulting with on the second of her chances before taking the game at the third opportunity when the American netted a forehand.

From there it was all uphill for Oudin, falling 0-40 behind in the next game with Wozniacki adding insult to injury by taking the game thanks to another net cord to go 4-2 up.

Wozniacki held serve and Oudin could do nothing to stop the Dane's momentum losing serve and the match in the next game.

Wickmayer, meanwhile, said she was staying calm about her surprise progress to the semi-finals.

The Belgian teenager, ranked 50th in the world, had not previously got past the second round of a grand slam event but she reached the last four with a straight-sets win over Ukraine's Kateryna Bondarenko at Arthur Ashe Stadium.

The 19-year-old now becomes the second Belgian to reach this year's semi-finals, joining former world number one Kim Clijsters in the last four.

Wickmayer defeated Bondarenko, ranked two places below her, 7-5 6-4, coming from 4-1 down in the second set to win her first grand slam quarter-final.

"It has surprised me in one way," Wickmayer said. "I have been felling really well the last few weeks.

"I've been playing a couple of great matches and I'm really playing with a lot of confidence.

"Coming here I was feeling pretty good and physically and mentally really strong ...but if it's the first great grand slam you've played, when you get to the third, fourth round you start surprising yourself.

"But actually, I've been staying pretty calm. I've worked really hard for this."

Wild card Clijsters is set to play her semi-final against defending champion and second seed Serena Williams, the only player from the top eight left in the women's draw. Both semis are scheduled for Friday.