(CNN) -- Serena Williams underlined her status as the overwhelming favorite for the women's U.S. Open title with a crushing "double bagel" win over Carla Suarez Navarro in the quarterfinals of the New York grand slam. 

The defending champion, bidding for a fifth singles triumph at Flushing Meadows, beat the Spanish world No. 20 6-0 6-0 to become the first woman since Martina Navratilova in 1989 to win a women's U.S. Open quarterfinal without losing a game. 

"I played well -- I played really well," world No. 1 Williams told the WTA's official website. "I was just more focused than anything. 

"I like to believe there is always room for improvement though. I haven't really thought about it yet, but off the bat, I think it was very difficult to hit a big serve today because of the winds, and I didn't get my serve up as much as I wanted to. But I don't know. I do think I definitely played well tonight." 

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The American's latest commanding win means she has lost just 13 games at the tournament ahead of her semifinal meeting with Li Na, who is appearing in the last four of the year's final grand slam for the first time after beating Russia's Ekaterina Makarova. 

"I'm still in the tournament and I'm not thinking like, 'I'm really dominant now'," added Williams. "I'm thinking I have a really tough match in the next round and want to do well." 

Earlier in the day second seed Victoria Azarenka, beaten by Williams in the 2012 final, won her delayed fourth round match against former world No. 1 Ana Ivanovic. 
Did she play as good as she is capable of playing?
"I like to believe there is always room for improvement though. I haven't really thought about it yet, but off the bat, I think it was very difficult to hit a big serve today because of the winds, and I didn't get my serve up as much as I wanted to. But I don't know. I do think I definitely played well tonight."