The 20-year-old had never previously appeared in the main draw of any of the four Slams, qualifying automatically courtesy of a WTA ranking that rocketed from 258 at the start of 2025 to her current rank of 81.
Marčinko had entered nine separate Grand Slam qualifying draws and never progressed beyond the second of three rounds, most recently falling to Alina Charaeva in the second round of qualifying at the 2025 US Open.
She faced 38-year-old German veteran Tatjana Maria, almost exactly one year to the day after losing to Maria at an ITF event in Bengaluru, and exacted revenge in the best possible way: by breaking serve on consecutive occasions in the second set to win in straights.
In 30 degree conditions aided by a cooling breeze, Marčinko wrapped up the match in 99 minutes and ran her veteran opponent ragged, dominating the net by winning 85% of her approaches into the front of the court.
Congratulations, Petra - your first Grand Slam win! How are you feeling after a few moments to reflect on this achievement?
"I'm feeling amazing. It's a big thing for me. I've played many Grand Slam qualifiers and never got into the main draw, so to win a match in the main draw is a big thing. I'm very happy."
There's no better place than a Slam to enact revenge on someone with a winning record over you. What were you expecting from Tatjana heading into the game and did you adapt your own game in response?
"I knew how she plays. It's really tricky to play against her. She has a bit of unusual tennis and I was ready for that. I changed a few key things. I was also physically better so I could endure more and I was serving better so a few things went my way today."
And to do it in such a remarkable back-and-forth second set where you were broken twice and then broke serve twice yourself to close out the game. What does that do for your confidence going into your maiden second round appearance at a Grand Slam?
"It means a lot. I was really short of some mental strength so I'm really happy I could lift today. It helps a lot."
By default, that means you'll now have to declare the Australian Open to be your favourite Slam! Are these acrylic hard court surfaces the most favourable for your style of play?
"For me, it depends. These courts really suit me. Sometimes it's clay, sometimes it's hard, but it doesn't really make a big difference. I do love Australia as well (though)."
You'd be quite used to having to play on back-to-back days on the ITF circuit and in Grand Slam qualifiers. What will your recovery routine be like knowing you've got at least one day off until the second round?
"I'm going to see when I play (next), but it's really good with Grand Slams to have a day in between. I think I'm going to practice a bit easier tomorrow and do only a few things today."