Melbourne: Serena Williams admitted she was frustrated and not at her best as she fought off a stubborn Tamara Zidansek to reach the Australian Open third round on Wednesday.
The American great, one short of Australian Margaret Court's all-time record of 24 Grand Slam titles, faces China's 27th seed Wang Qiang next in Melbourne.
The 38-year-old Williams was never in serious trouble against the 70th-ranked Slovenian Zidansek, winning 6-2, 6-3 at Rod Laver Arena.
But the eighth seed was restrained in her celebrations and said: "It was a good match for me, she was a really good fighter, she did not just let me win."
The 22-year-old Zidansek put up resistance in the second set with Williams twice failing to break when 40-0 up on the Slovenian's serve.
Williams then struggled through her own service game at 3-2 down, with a brief stoppage while the roof closed because of more rain in Melbourne.
Williams finally broke Zidansek's stubborn resolve in the seventh game, getting the break of serve on the way to victory in one hour 18 minutes.
The American great described herself as "frustrated" by her failure to bury her opponent in those two service games.
"I made so many errors in a row and had to battle through my own internal problems," said Williams.
"I knew I had to play better and couldn't keep making unforced errors like that, otherwise it was going to be a long evening for me."
Williams, who has won the Australian Open seven times, thrashed Wang 6-1, 6-0 when they met at the US Open quarter-finals last year.
She dropped just three games in her opening win over Russian teenager Anastasia Potapova on Monday in Melbourne.
SANDGREN STUNS BERRETTINI
Tennys Sandgren sent eighth seed Matteo Berrettini packing from the Australian Open Wednesday as the American eyes another strong performance after his scandal-marred run to the 2018 quarter-finals.
Berrettini, last year's US Open semi-finalist, slumped to defeat in a five-set marathon which finished 7-6 (7), 6-4, 4-6, 2-6, 7-5 in 3hrs 23 mins -- the highest ranked seed to fall so far.
It was a disappointing end for the Italian, who reached the US Open semi-finals and stormed up the rankings last year, reaching a new career-high 10 times.
"It was a top-10 win in a Slam so I'd say it's up there," said Sandgren. "I'm not sure where it lies in the ranking list but pretty high."
Sandgren, a devout Christian, achieved his best Grand Slam result at Melbourne Park in 2018 but it was overshadowed by controversy over his political views and links to right-wing activists.
Sandgren was forced to wipe the slate clean, deleting years of social media postings.
Among his tweets, Sandgren had appeared to back a debunked online conspiracy in 2016 which linked Hillary Clinton to a supposed child sex abuse ring at a Washington pizzeria.
He also retweeted a video from white nationalist Nicholas Fuentes.
Sandgren did not want to comment on the 2018 episode after his Berrettini win, but acknowledged the experience "had helped me with my game".
Ranked 100, he said he played better at the Slams, having made the fourth round at Wimbledon last year and the third round at the US Open.
"I had some good weeks at the Slams last year. I like these tournaments a lot where it feels like one of the few weeks where it actually feels like it means something," he said.
"You know, sometimes you get lost when you're travelling a lot and playing 30 or 35 weeks a year -- I certainly get lost out there sometimes, so I feel my game kind of comes together at these types of weeks.
"And I just feel fresher in January."
His reward for beating Berrettini is a third-round clash against fellow American Sam Querrey.