Coming back from a right wrist injury and an appendix operation that sidelined him for much of last season, and coming off a rare first-round loss in a tune-up event in Doha, the 14-time major winner said he had concerns about his fitness coming into the first Grand Slam tournament of the year.
He didn't show it, hitting 37 winners, breaking Youzhny twice in each set, holding his own serve comfortably and fending off the only break-point chance he faced.
"Last year, second half of the year had been tough mentally, tough physically for me," he said. "I played four matches in the last seven months — that's not enough to be back with confidence."
He said the loss to Michael Berrer in Doha earlier in the month was another dent to his confidence.
"When that happens after a tough period of injuries you arrive here with doubts," he said. "This first match was tough mentally for me — (I) hope this match will give me confidence to play well next round.
"My serve worked well, the return, and I played with not many mistakes."
Nadal hasn't won the Australian Open since 2009, but has reached the final in his last two trips to Melbourne Park, losing to Novak Djokovic in a 5-hour, 53-minute epic in 2012 and to Stan Wawrinka last year.
No. 2-ranked Roger Federer, who won the last of his four Australian titles in 2010, got a good workout in the first night match on Rod Laver Arena before beating Lu Yen-hsun of Taiwan 6-4, 6-2, 7-5.
Three-time Australian Open finalist Andy Murray began his quest for an elusive Australian title with a 6-3, 6-4, 7-6 (3) win over Indian qualifier Yuki Bhambri.
No. 7-seeded Tomas Berdych beat Alejandro Falla 6-3, 7-6 (1), 6-3, No. 10 Grigor Dimitrov defeated Dustin Brown 6-2, 6-3, 6-2, No. 14 Kevin Anderson had a 7-6 (5), 7-5, 5-7, 6-4 win over Diego Schwartzman, and No. 20 David Goffin beat 36-year-old Michael Russell, the oldest player in the men's draw, 6-3, 6-3, 5-7, 6-0.
Also advancing on the men's side were No. 22 -seeded Philipp Kohlschreiber, No. 24 Richard Gasquet, No. 29 Jeremy Chardy and No. 32 Martin Klizan. No. 15 Tommy Robredo made an early exit when he retired with a groin strain after five games against Edouard Roger-Vasselin.
Eight of the seeded players in the women's draw tumbled out on day one, while No. 3 Simona Halep and No. 6 Eugenie Bouchard advanced in straight sets.
Halep opened play on the main court with a 6-3, 6-2 win over Karin Knapp and Bouchard, who reached the semifinals or better at three majors last year, beat Anna-Lena Friedsam 6-2, 6-4 in a night match on the renovated Margaret Court Arena. No. 10 Ekaterina Makarova, No. 14 Sara Errani, No. 21 Peng Shuai and No. 22 Karolina Pliskova also moved into the second round.
No. 5 Ana Ivanovic was the highest-ranked of the first-round losers, struggling with her serve in a 1-6, 6-3, 6-2 loss to Czech qualifier Lucie Hradecka in the first big upset of the tournament.
Irina-Camelia Begu defeated No. 9 Angelique Kerber 6-4, 0-6, 6-1, Yanina Wickmayer beat No. 23 Anastasia Pavlyuchenkova 4-6, 6-3, 6-3 and Caroline Garcia beat No. 27 and two-time major winner Svetlana Kuznetsova 6-4, 6-2. No. 16 Lucie Safarova (16), No. 17 Carla Suarez Navarro, No. 28 Sabine Lisicki and No. 32 Belinda Bencic were also defeated on the opening day.
American Christina McHale was sick on court and saved a match point as she rallied to beat Stephanie Foretz 6-4, 1-6, 12-10.
Former No. 1-ranked Ivanovic, who had a tour-leading 58 match wins in 2014 and started this season by reaching the final at the Brisbane International, had 10 double-faults and made 30 unforced errors.
"The whole match I didn't really feel like myself out there," Ivanovic said. "It's probably the worst thing could happen. But still, the year is young and I really have to now sit and work on few things and just maybe try to have a different approach to this kind of event and try to see what was lacking."