(CNN) Comebacks were the order of the day at the Australian Open.
Novak Djokovic, Maria Sharapova, Stan Wawrinka and Petra Kvitova all returned to Melbourne Park and all but one reached the second round Tuesday ahead of one of the city's summer heat waves. In a roller-coaster ride not unusual for a Kvitova match, the twice Wimbledon champion fell 6-3 4-6 10-8 to Andrea Petkovic in nearly three hours.
Djokovic fared better. He is the undisputed King of Melbourne, with six of his 12 grand slam titles capped in glory at Rod Laver Arena.
Amid sunshine in hot but not overpowering conditions on the second day of the fortnight, the Serb cruised past American Donald Young 6-1 6-2 6-4 -- on the secondary Margaret Court Arena -- in his first official match since being sidelined with an elbow injury at Wimbledon in July.
The Serb sported a grey sleeve on his serving arm and owns a new, abbreviated service motion, one that lessens the impact on his right elbow.
There is, noticeably, less take back and serve rotation, but Djokovic didn't seem bothered as he faced a mere two break points. His first serve speed, too, averaged around 114 miles per hour, higher than his figure when he won the US Open in 2011 and Madrid Masters in 2016, for example.
Djokovic said before the tournament that surgery wasn't out of the question if he experienced discomfort in the future but simply judging by Tuesday's performance, he looked sharp. Playing several matches, though, will provide a different test.
It was just a week ago that his participation in Melbourne looked in doubt after skipping an exhibition in Abu Dhabi and pulling out of Doha as the defending champion.
"I did have various emotions, mostly good ones," said Djokovic, whose ranking has dropped to 14th. "Excitement, joy, gratitude for being able to have an opportunity to compete. Not a while ago, about three weeks ago, I didn't know whether I'm going to play Australia or not.
"I was looking forward to get out on the court and compete. I did feel nerves and I did feel a bit skeptical whether I'm going to be able to continue playing well as I have the last couple weeks in the practice sessions.
"But I thought I controlled it well. I didn't get carried away by anything, even though I was a couple times in the match that things could have maybe gotten different way and different direction. I just didn't allow it to happen. Very, very solid performance."
Djokovic spent as much time in his post-match media conference discussing a players' meeting last week, one in which he reportedly said that the players should seek more prize money at grand slams and set up a separate players' union. Those are issues that have surfaced in the past in men's tennis.
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According to the Daily Mail, Djokovic asked ATP officials who were present -- that is standard -- to leave the meeting and brought a lawyer with him. The newspaper also said boycotting next year's Australian Open was an idea that was mentioned.
Djokovic -- who encounters another player affected by injury, Gael Monfils, in round two -- refuted much of the claims.
"I saw that you've portrayed me as someone who is very greedy, asks for more money and wants to boycott," Djokovic told reporters.
"What happened is that we players just wanted to have us players talk about certain topics. I don't think there is anything unhealthy about that. We get together, 100 players get together two or three times in a whole year. This is one of the places where we get together.
"We wanted to use this opportunity to speak about certain subjects and see how everyone reacts to that, and I guess see what opinions are. There was no decisions being made. There was no talks about boycott or anything like that."
You could have been forgiven for thinking that Sharapova was playing herself Tuesday, glancing at the TV scoreboard accompanying her match -- she was facing Germany's Tatjana Maria and won comfortably 6-1 6-4.
It was two years ago that Sharapova tested positive for meldonium at the Australian Open and ultimately served a 15-month ban. She is still searching for top form after being limited to eight tournaments when she returned to the circuit in 2017.
"I feel like I'm building," the five-time grand slam winner told reporters. "I feel like with every tournament and every week I have different feelings about different things. Some things are coming a little slower than I wanted. Some things I feel good about.
"Still feel like I'm building physically and getting the match play in. I'm motivated to, with every week, to keep taking in what I have learned from that week and using it to my advantage in the following tournament. As long as I have that in my mind, it's okay."
The unseeded Sharapova faces a tough challenge in the second round against 14th seed Anastasija Sevastova, who beat the Russian at the US Open prior to the tables being turned in another marathon in Beijing.
Wawrinka -- the 2014 champion in Melbourne -- sported a scar on his surgically repaired left knee as he, too, contested his first match since Wimbledon but battled past Ricardas Berankis 6-3 6-4 2-6 7-6 (7-2).
"I still have some pain," said the Swiss. "It depends the way I'm moving, how I push on it. In general, it's going the right direction. That's the best news."
The news wasn't as good for Kvitova, who missed last year's tournament after she was attacked in her home by a knife-wielding intruder and needed surgery on her left, playing hand. Her career was in jeopardy.
Kvitova appeared to be on course for victory Tuesday when she saved three match points at 4-5 in the third set. Unable to serve the contest out once, Kvitova got another chance at 8-7. But leading 15-0, Kvitova missed a short forehand into the net with Petkovic completely out of position and never recovered.
A former world No. 9, Petkovic could battle world No. 1 Simona Halep in the third round. Halep won in straight sets over 17-year-old Australian wildcard Destanee Aiava 7-6 (7-5) 6-1 but it was far from smooth for the popular Romanian.
Halep trailed 5-2 in the opener -- having to save two set points -- then hyper-extended her left leg and rolled her left ankle in the same motion in the second set.
Halep next meets Eugenie Bouchard, with the Canadian ending a nine match losing streak by topping Oceane Dodin 6-3 7-6 (7-5).
Although Bouchard has struggled since her breakout year of 2014, the former Wimbledon finalist defeated Sharapova in Madrid in a "grudge match" last year.
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Men's defending champion Roger Federer, meanwhile, began his tournament by easing past Slovenia's Aljaz Bedene 6-3 6-4 6-3.
The 19-time grand slam winner was subsequently interviewed by comedian and actor Will Ferrell, a tennis fan.
Keeping with the comeback theme, 2009 US Open winner Juan Martin del Potro overcame American Francis Tiafoe 6-3 6-4 6-3 in his first Australian Open appearance since 2014.
Del Potro sits in Federer's quarter, having beaten his Swiss rival at the US Open in September.