Serena still 'in love' with tennis as 24th Slam title beckons
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The 39-year-old had 31 unforced errors but wore down Russian Anastasia Potapova 7-6 (7/5), 6-2 in 97 minutes on Rod Laver Arena to set up a clash with seventh seed Aryna Sabalenka of Belarus.
"I think if I didn't love it, I wouldn't be sitting here. I wouldn't be in Australia if I didn't love what I do," she said when asked how she kept her focus after so many years, having made her Australian Open debut in 1998.
The 10th seed had been in strong form so far in Melbourne as she chases Margaret Court's record 24 Grand Slam tally, but was out-of-sorts in an error-strewn start to fall down a break.
But Potapova, 19, had a meltdown trying to serve out the first set with five double faults squandering the golden opportunity.
A refocused Williams then lifted her intensity and won a tiebreak before cruising through the second set.
"It was good to get through that match. The first set was extremely tight," she said.
"I was a little tight, but it worked out. Was able to play a little more free in the second set."
Williams, the seven-time Australian Open champion, will on Sunday play Sabalenka who thrashed American Ann Li 6-3, 6-1, with a place in the quarter-finals at stake.
That match will be played with no fans in the stadium after Melbourne was ordered into a snap five-day lockdown from midnight to counter a new coronavirus cluster, with players entering a biosecure "bubble".
Williams said she had been enjoying the buzz of having spectators back, as they have been for the opening five days.
"It's not ideal. It's been really fun to have the crowd back, especially here. It's been really cool," she said. "But, you know what, at the end of the day we have to do what's best. Hopefully it will be all right."