It's new and exciting for Andy Murray and Angelique Kerber, entering a Grand Slam tournament with the No. 1 in front of their names.
Both reached the top of the rankings for the first time near the end of 2016, ending long reigns by Novak Djokovic and Serena Williams.
And so they'll open their Australian Open campaigns on Rod Laver Arena on day one — both against Ukrainians.
Murray, a five-time runner-up, opens his pursuit of a first Australian title against Illya Marchenko in the last day match on the main show court. Kerber opens the night session against Lesia Tsurenko. She'll be followed on court by Roger Federer, who is returning from six months on the sidelines.
The 'one-round-at-a-time' cliche is well worn in tennis. For Kerber, though, it's pertinent. Seeded seventh last year, the left-handed German had to save a match point in the first round against Misaki Doi. Spurred on by that, she went on to beat Serena Williams in the final and claim her first Grand Slam title. She added a second major at the U.S. Open and ascended to the No 1 ranking.
"I think this point where I was match point down, that was the important point for my career," Kerber said Sunday, speaking of her first-round escape against Doi. "You never know (if) I lost the match, what would have happened."
It gave her the freedom to play without pressure, and that made all the difference.
"When I'm looking back, I was feeling that I got a second chance to stay in the tournament," she said. "I was playing since then without expectation ... just enjoying everything."
Kerber can hang on to the top ranking by reaching to the final here, but she's already feeling there's more to defend than her title.
"It's a new challenge for me, for sure," she said. But, "We are starting from zero here. I have to be ready from the first round again.
"I will try to not put too much expectation and pressure on myself. I mean, I will try to do it like last year — that was the way I had my success."
Record-chasing, six-time champions Djokovic and Williams, seeded No. 2 and anchoring the bottom half of the men's and women's draws, won't be in action until day two. Djokovic is aiming to be the first man to win seven Australian titles. Serena Williams is chasing an Open-era record 23rd major title.
Newly-engaged Williams hasn't wanted to talk about the record, being a little bit superstitious. Williams is concentrating on her first-round match against Belinda Bencic, who was seeded 12th here last year and who beat her in Toronto in 2015.
While Serena has to wait, the Williams family will be represented on Rod Laver Arena on Monday by her older sister, Venus. The 13th-seeded Venus Williams will play against Kateryna Kozlova following fourth-seeded Simona Halep's opener against Shelby Rogers.
French Open champion Garbine Muguruza starts play on Margaret Court Arena against Marina Erakovic, and U.S. Open champion Stan Wawrinka opens the night session on the second show court.
Fifth-seeded Kei Nishikori gets things underway against Andrey Kuznetsov on Hisense Arena, where Nick Kyrgios will make his return to the tour against Gastao Elias.
The 21-year-old Kyrgios finished 2016 under a ban in a season overshadowed by clashes with officials and fans and by the tanking at the Shanghai Masters which led to an eight-week suspension.
The ban was reduced to three weeks when Kyrgios agreed to consult a sports psychologist, allowing to warmup for the Australian Open at the Hopman Cup.
That's where Federer made his return from six months out to give his injured left knee time to heal. The 17-time major winner didn't play after Wimbledon and his ranking slid to No. 17 by this week. That resulted in him getting a tougher draw than usual at the tournament he has won four times, and where he has reached the semifinals in 12 of the last 13 years. If results go with rankings, he'll play two qualifiers before a potential third-round match against No. 10 Tomas Berdych. Nishikori and Murray are also in his quarter.
Federer will open against another 35-year-old veteran, former No. 8-ranked Jurgen Melzer.
"That's the part of the draw I care most about because of having not been playing," Federer said.
Wild-card entry Destanee Aiava, a 16-year-old Melbourne high school student, is set to become the first player born in this millennium to play a main draw match at a Grand Slam when she meets German qualifier Mona Barthel on Show Court 2.