"I had a great week in Brisbane. Of course, I'm confident," Svitolina said.
"But I try to take it one match at a time, be really focused on my game, and don't have, like, crazy thoughts in my head.
"You have lots of different kind of pressure when you're playing Grand Slam - from the media, from expectations from everyone.
"Sometimes you're really, like, not focusing on your game and just playing, just playing not 100 per cent.
"You're not focused on your game plan, you're not ready to compete. Yeah, just all over the place. It can happen."
Svitolina opens her campaign today against a qualifier, while the top-seeded Halep plays tomorrow, respectful of 17-year-old Australian wildcard playoff winner Destanee Aiava.
Incredibly, Halep will try to net her elusive first slam without a sponsor after ending her association with adidas at the end of last year.
The Romanian will don her "lucky" red dress she ordered herself and sported during her charge to the title in Shenzhen to kick-start 2018 in style.
Twice a runner-up at Roland Garros, Halep has crashed out in the first round the past two years at Melbourne Park.
"I can say I started the year better. I am more relaxed," Halep said.
"I'm enjoying more the time on court. I just sometimes try to change something in my game, to adjust, to improve.
"So my focus is on other stuff now than the ranking or to win the match."
Halep's French Open final vanquisher Ostapenko - up against Francesca Schiavone in the first match on centre court - and 2017 runner-up and fifth seed Venus Williams, who is in the marquee first-round encounter with Swiss ace Belinda Bencic, are among the other women's big names playing today.
Rod Laver Arena
7-Jelena Ostapenko (LAT) v Francesca Schiavone (ITA)
5-Venus Williams (USA) v Belinda Bencic (SUI)
3-Grigor Dimitrov (BUL) v qualifier
Night
1-Rafael Nadal (ESP) v Victor Estrella Burgos (DOM)
23-Daria Gavrilova (AUS) v qualifier
- AAP