NEW YORK (AFP) – Ruthless defending champion Serena Williams breezed into the U.S. Open semi-finals to book a showdown with Chinese fifth seed Li Na, who fought off nerves to battle her way into the final four.

World number one Williams, a 16-time Grand Slam winner seeking her fifth U.S. Open crown and her ninth title of the year, on Tuesday dispatched 18th seed Carla Suarez Navarro 6-0, 6-0, in 52 minutes on the Spaniard’s 25th birthday.

“I’m so happy to be in the smei-finals. It really feels great,” Williams said.

Li, the 2011 French Open champion, overcame nervous feelings for a 6-4, 6-7 (5/7), 6-2 victory over Russian 24th seed Ekaterina Makarova.

Reigning French Open champion Williams is 8-1 all-time against Li but was tested 7-5, 7-5 in their most recent matchup last month in a U.S. Open run-up semi-final at Cincinnati.

“She is playing some of the best tennis of her career,” Williams said. “It’s going to be a tough match.”

Williams, who has dropped only 13 games in five matches on the New York hardcourts, matched the worst rout in U.S. Open women’s quarter-final history, Martina Navratilova’s 6-0, 6-0 blanking of Bulgarian Manuela Maleeva in 1989.

Ignoring a fan’s call to let the birthday girl win at least one game and a few boos when she did not, Williams showed no mercy in taking only 52 minutes to complete the rout on a windy night at Arthur Ashe Stadium.

“She’s a great player,” Williams said. “The conditions were so tough. It was definitely not her best tennis today. Only because I’ve been playing here for like 50 years, I’ve kind of gotten used to the conditions.”

No Spaniard has beaten a top-ranked woman since 2001 but Suarez Navarro, who has never taken more than three games off Williams in a match, did become the first Spanish woman in a U.S. Open quarter-final since Arantxa Sanchez Vicario in 1998 and made $325,000 in prize money for a last-eight exit.

Li seized a 4-2 tie-breaker lead but lost five of the next six points, three of them including the last with forehands beyond the baseline, and had to rally by breaking Makarova’s last two service games in the third set.

“I’m not so happy,” Li said. “Today was the first time I was feeling so nervous. I was happy because at least I was fighting a lot on the court.

“Didn’t play the best of tennis but I still fought am still in the tournament.”

Either Williams or Li, this year’s Australian Open runner-up, would become the oldest women’s champion in U.S. Open history at age 31 with a triumph in Sunday’s championship match.

At least one other over-30 semi-finalist is assured, matching Wimbledon in 1994 with three over-30 players in the last four, a record that would fall if 48th-ranked Daniela Hantuchova upsets Belarus second seed Victoria Azarenka in a Wednesday quarter-final.

Two-time Australian Open winner Azarenka reached the last eight by beating Serbian 13th seed Ana Ivanovic 4-6, 6-3, 6-4 in a match postponed from Monday due to rain.

Azarenka took advantage of Ivanovic’s 42 unforced errors and broke the fellow former world number one nine times in the match, advancing despite surrendering seven breaks herself and hitting just 21 winners.

“There’s a lot of room to improve, but I don’t think that my serve was a deal breaker of those games I lost,” Azarenka said.

Ivanovic and Azarenka exchanged seven breaks in a row at one stretch.

“I put her a lot under pressure,” Ivanovic said. “I felt like I could break her, but it was very frustrating that I was losing my serve constantly.”

Azarenka, who lost to Williams in last year’s U.S. Open final, has split four career matches with Hantuchova.

“She’s playing the best tennis of her life,” Azarenka said. “She is really playing well and has a lot of confidence. We hit with each other a lot so there will be no surprises there.”

Azarenka, a semi-finalist in five of the past seven Grand Slams, defeated world number one Williams in the final at Cincinnati in the last big U.S. Open tune-up event, securing her role as the main threat to Williams’ reign.

Ivanovic fired 17 winners in the first set and had 15 forehand winners before Azarenka managed one.

“I’m not concerned about the slow start,” Azarenka said. “It’s just a matter of getting that groove. I just have to be a little more focused on those opportunities I have.”

Photo Credit: AFP/Emmanuel Dunand