Opelka said that the match with Nadal was not really in his mind, but "in any case, I needed to prepare more so that (Fogini) wanted to win and believe in himself that he could win".
Djokovic, though, was not to be denied a 900th ATP career victory and the Serb star told reporters: "I actually like tough first rounds in grand slams particularly".
Former champion Maria Sharapova said she was unsure if she would be back at the Australian Open next year after the wild card suffered a third successive first-round exit at a Grand Slam.
Nadal pushed the Bolivian Hugo Dellien aside in 6-2, 6-3 and 6-0 in just over two hours to advance to the second round.
The Spaniard had a great 2019 as well, where he won two Grand Slams and finished the year as the top-ranked men's tennis player. "Round-by-round, point-for-point mentality. I know other guys that are playing extremely well right now so I think it's just important to stay very calm about things right now", he added. Vekic rallied back in the second set from a 4-1 hole, too, to secure the match in 81 minutes. "That's my goal, to win as many Grand Slams as possible, but for today my mission was to win". If he does that, the titles will take care of themselves.
The six-time Australian Open champion defeated Steve Johnson 6-3, 6-2, 6-2 to race into the second round.
"It helps me to come into the tournament with more confidence".
"I'm just so happy I didn't have any setbacks (in the pre-season)".
Fourth person dies in China's Wuhan from novel coronavirus
The World Health Organisation began responding to cases of unexplained pneumonia in Wuhan, central China, on December 31, 2019. SARS, possibly originating in bats, emerged that year and raged in China and then spread worldwide, killing 774 people.
The world No.1 won the first five games and then the last eight in a 6-2, 6-3, 6-0 triumph on Rod Laver Arena on Tuesday.
France's Jo-Wilfried Tsonga, the 2008 runner-up, was forced to retire from his match against Alexei Popyrin due to an injury while trailing the Australian 6-7 (5-7) 6-2 6-1.
World No 1 Rafael Nadal started his campaign after displaying his dominance over Bolivia's Hugo Dellien.
Caroline Wozniacki, playing in the final tournament of her career, eased past American Kristie Ahn 6-1 6-3 while Romania's Sorana Cirstea stunned 32nd seed Barbora Strycova 6-2 7-6 (5) before rain brought a halt to proceedings on the outer courts.
Medvedev, the narrow loser to Nadal in September's US Open final, dropped the second set against Tiafoe before recovering to win 6-3, 4-6, 6-3, 6-2.
Britain's Johanna Konta, a two-time Slam semi-finalist, also fell at the first hurdle as she battles to overcome a knee problem, losing 4-6, 2-6 to unseeded Tunisian Ons Jabeur.
Play got underway on all courts on time although the Bureau of Meteorology has forecast heavy rain throughout the day with a high of just 21C (69.8°F).