* Belarusian to play Pennetta in semis
* Nadal overwhelms fellow Spaniard Robredo
* Gasquet ousts Ferrer, to meet Nadal in semis (Adds Nadal victory, ends Day 10)
By Larry Fine
NEW YORK, Sept 4 (Reuters) - Victoria Azarenka struck a blow for the younger generation by beating Daniela Hantuchova of Slovakia 6-2 6-3 to join a trio of 31-year-olds in the semi-finals of the U.S. Open on Wednesday.
The 24-year-old Belarusian, the second seed and runner-up last year, will play unseeded Italian Flavia Pennetta, while defending champion Serena Williams meets Li Na of China in Friday's semi-finals.
Pennetta reached her first grand slam semi-final on Wednesday by beating longtime friend and Fed Cup team mate Roberta Vinci, the 10th-seeded 30-year-old, 6-4 6-1.
On the men's side second seed Rafa Nadal continued his remarkable 2013 form, improving his hardcourt record to 20-0 with a 6-0 6-2 6-2 hammering of fellow Spaniard Tommy Robredo.
Next up for Nadal is France's Richard Gasquet, who will be playing in the semi-final stage of a slam for the first time since Wimbledon in 2007.
Azarenka is well aware she is battling the 'old guard' in last four.
"I'm a baby, what can I say?" she added. "It's amazing to see such great players in the semi-finals."
The victory moved Australian Open champion Azarenka one step closer to a possible Arthur Ashe Stadium rematch against Williams for the title.
"It's amazing to see athletes doing so well, their careers longer so fans and themselves can enjoy their careers much better," she said. "Everybody looks much fitter, really taking care of their body and taking the sport to the next level."
Robredo had spoiled what would have been the first meeting at the U.S. Open between Nadal and all-time grand slam king Roger Federer after the 31-year-old Spaniard sent the Swiss master packing in straight sets in the fourth round.
Nadal, who has come back from knee injuries that sidelined him for seven months to win nine tournaments including his eighth French Open for his 12th grand slam crown, bounded for joy after steamrolling another opponent at Arthur Ashe Stadium.
"I think I played my best match in the U.S. Open this year," said 2010 U.S. Open winner Nadal, who has lost just one set from five matches. "Playing a little bit better every day is great."
Eighth-seeded Gasquet booked his long awaited return to the last four of a men's slam with a 6-3 6-1 4-6 2-6 6-3 upset of fourth seed David Ferrer of Spain.
It was the second successive five-setter for the 27-year-old Gasquet, who clinched the concluding set of a marathon fourth-round match against big-serving Canadian Milos Raonic 7-5.
Gasquet had lost eight of nine previous matches against Ferrer. The hill could be even steeper against Nadal, who has won all 10 of their professional encounters.
"Rafa, I never beat. Last time I beat him I was 13-years-old," said Gasquet. "That was the only time I beat him. He's a good friend of mine. I have nothing to lose."
Playing in just the second grand slam quarter-final of his career, 27-year-old Gasquet went all out against Ferrer, using his trademark one-handed backhand to near perfection as he closed him out in three hours and 23 minutes.
Gasquet broke the Spaniard, a model of consistency with trips to the quarters or better in the last eight slams, on a double fault at break point for a 4-2 lead in the fifth set.
He ended it with a bristling forehand for his 52nd winner.
"I was a little nervous about getting into the semis at the U.S. Open, but I did it. Was a big win for me," Gasquet said.
Pennetta, ranked 83rd as she battles back from surgery on an injured right wrist that kept her out of last year's tournament, said times had changed for veteran players on the women's side.
"I think we just keep playing. Before the career of the woman was shorter, they retired early," Pennetta said.
"It's good to stay physical, in a good way, and play this good tennis at this age. I'm proud of me now."
The good-natured match between friends who have competed against one another since they were 10 turned into a rout by the second set, which Pennetta raced through in 24 minutes against an error-prone Vinci.
"It was, of course, a special day for us," said Vinci, who is part of the world number one ranked women's doubles team with fellow Italian Sara Errani, and still busy defending their U.S. Open double title.
"This time she won, but I think that I'm happy, too, about this tournament."
Pennetta continued a strong history of success at Flushing Meadows.
After advancing to the quarters in 2008, 2009 and 2011, Pennetta has not dropped a set in her march to the semi-finals, dropping just 25 games in her five victories.
"I don't know. I just enjoy to play here," she said.
Their quarter of their draw was something of a festival for the Italians.
In playing Pennetta, Vinci was facing her third successive compatriot, having beaten unseeded Camila Giorgi and Karin Knapp in previous rounds. Pennetta eliminated fourth seed Errani in the second round. (Editing by Frank Pingue and Nick Mulvenney)