The Associated Press Madison Keys of the U.S. serves to Oleksandra Oliynykova of Ukraine during their first-round match.

MELBOURNE, Australia — Defending champion Madison Keys struggled early but held on to defeat Oleksandra Oliynykova of Ukraine 7-6 (6), 6-1 in a first-round match early today at the Australian Open.

Ninth-seeded Keys dug herself into a deep hole at Rod Laver Arena but recovered. She trailed 4-0 in the first set and rallied to force a tiebreaker against the Ukrainian.

Oliynkyoka, playing in her first Grand Slam main draw, also raced to a 4-0 lead in the tiebreaker but failed to cash in on two set-point opportunities, giving Keys the opening she needed to take the set.

“Obviously I was very nervous at the start,” Keys said in an on-court interview. “As nervous as I was . . . I’m really glad to be back, and that I got through that match.”

Keys praised Oliynykova, who signed autographs, accepted loud applause, and waved a Ukrainian flag on-court after the match.

“My opponent today was incredible,” Keys said. “She started so well. Such a great competitor. She definitely made it tricky for me.”

The first set lasted 1 hour, 12 minutes.

Oliynykova kept Keys off stride, particularly in the first set, with random shots, which included high lobs — moon shots — that forced Keys deep behind the baseline. The Ukrainian’s strong defense and unorthodox play also kept her in the match early.

“It’s definitely not the typical style that you see every day, which makes it a little bit trickier,” Keys said.

She lauded Oliynykova’s “change of pace with the higher balls and the slice. She’s also super fast and got to a lot of balls.”

Keys’ rally in the first set clearly took energy from the Ukrainian, who slowly became overwhelmed by the defending champion’s power and pace.

Keys is playing in her 12th Australian Open and her 50th Grand Slam tournament overall.

Among other early matches today, two seeded women’s players were beaten. Indonesian Janice Tjen beat 22nd-seeded Leylah Fernandez of Canada 6-2, 7-6 (1) and Tereza Valentova of Czech Republic defeated Australia’s top-ranked women’s player, 30th-seeded Maya Joint, 6-4, 6-4.

Another Australian, Taylah Preston, beat Zhang Shuai of China 6-3, 2-6, 6-3.

On Monday, Novak Djokovic equaled two all-time tennis records by starting his 21st Australian Open. He added another milestone with his 100th win at Melbourne Park.

The 38-year-old Djokovic is now 100-10 at the Australian Open, where he’s won 10 titles. He also has won 102 matches at Wimbledon and 101 at Roland Garros. By starting his 21st Australian Open campaign, he equaled the tournament record held by Roger Federer.

Djokovoic won 6-3, 6-2, 6-2 over Pedro Martinez.