* First 'double-bagel' in US Open quarters in 24 years
* Needs just 52 minutes to set semi-finals date with Li (Adds quotes, details)
By Larry Fine
NEW YORK, Sept 3 (Reuters) - Defending champion Serena Williams walloped Spain's Carla Suarez Navarro 6-0 6-0 to race into the semi-finals of the U.S. Open on Tuesday.
Top seed Williams served up the dreaded "double-bagel" in a quick-fire 52 minutes to set up a clash with fifth seed Li Na, who earlier became China's first U.S. Open semi-finalist by beating Russian Ekaterina Makarova.
"Honestly she's a great player," said Williams, blaming windy conditions for the Spaniard's plight on her 25th birthday.
"The conditions today were so tough. It was not her best tennis today."
The outcome may have been more about the world number one being at something close to her best, however.
Williams won 88 percent of her first serves, rifled in four aces, smacked 20 winners to three for her opponent, and won 53 points to just 18 for the 18th seed.
"I played really good. I was just more focused than anything," she added, stopping short of calling it her best. "I like to believe there is room for improvement."
It was only the second love-love victory in a U.S. Open women's quarter-final dating back to 1968, and first since Martina Navratilova subjected Manuela Maleeva of Bulgaria to the same embarrassment in 1989.
At 31, Williams is campaigning to become the oldest U.S. Open women's winner since tennis turned professional in 1968.
She has lost just 13 games from her five matches so far and said she has been balancing fun with work at Flushing Meadows.
"I'm having a blast this week," said Serena, who is also still alive in women's doubles with older sister Venus.
"I have just really been enjoying my matches. For me, I have to stay in that moment of fun, but intensity, but calm. If I can try to do those three things, it works out."
Suarez Navarro's consolation was a $325,000 check for being eliminated from her first U.S. Open quarter-final.
"I just want to go there and enjoy, but Serena was playing really, really good. I do everything I can," she said.
The Spaniard, who had ousted eighth-seeded Angelique Kerber of Germany in the fourth round, said the blustery conditions had made her task even more difficult.
"Serena is a strong player. When I play with the wind against me, I have no chance," said Suarez Navarro, who had hoped to rebound after the lightning-quick, 19-minute first set.
"I was thinking the situation can change, another set is a new set. But obviously, no."
(Reporting by Larry Fine; Editing by Ian Ransom/Peter Rutherford)