"It's been tough to get back to No. 1," he said. "I'm happy to have the chance to be in that position."
Federer out of Cincinnati with bad back; Nadal to be No. 1 →
"I'm very, very happy, being in the quarterfinal of a Grand Slam after couple of years not being there is very special for me," said Nadal, who won the Australian Open title in 2009 and was a finalist two other times.
Serena Williams, Nadal, look to book Australian Open semis →