The former world No.1 clinched the last of his 12 grand slam titles in 2016 and has dropped to 22 in the rankings after personal issues and elbow surgery affected his form and confidence.
The 31-year-old was pushed in his second-round match at Roland Garros before squeezing past Spanish qualifier Jaume Munar 7-6 (7-1) 6-4 6-4.
Afterwards the Serb remained philosophical about his tennis woes.
"To sit here and talk about how tough it is and you have people starving to death, for me there is no point talking about that [his issues]," he said.
"It's just the way it is. As an athlete I have to face these challenges."
Djokovic hasn't reached the semifinal of a grand slam since losing in the final of the US Open in 2016, the same year he clinched the Australian and French Open titles.
"I'm not playing at the level I wish to but I'm trying not to give up," said Djokovic, who showed glimpses of his old self before losing to Rafael Nadal in the semfinal of the Italian Open recently.
"At times I do lose maybe a comfort level on the court and confidence, and that's something that I'm still building gradually.
"The more matches I play, the better it is. The more I win, of course, the better it is."
Djokovic will next play 13th seed Roberto Bautista Agut.
'Success will come'
From one of tennis' established "Big Four" stars to one of the game's rising talents, but only the coming days will tell whether Alexander Zverev's marathon win Wednesday at the French Open could spark a grand slam breakthrough or be his downfall.
For the time being, the towering German is mightily relieved after seeing off Dusan Lajovic 2-6 7-5 4-6 6-1 6-2 in three hours, 24 minutes.
While Zverev has already made a name for himself on the tennis tour by climbing to third in the rankings and amassing three Masters titles by the age of 21 -- multiple Masters victories in the last decade have usually been reserved for the 'Big Four' -- he has yet to reach a grand slam quarterfinal. Or even defeat a top-50 foe at a major.
The paradox hasn't been lost on him.
But in downing the world No. 60 in mostly sunny skies in Paris, the second seed moved into the third round and thus a step closer to the benchmark last eight. Lajovic appeared to be struggling with cramp in the fifth set, helping to explain the 31-minute final frame.
"Everybody tries to make a bigger story out of it than it is," Zverev told reporters. "I'm not worried. I know if I'm doing the right things and if I do the right work I'll win those long matches, and the success will come itself. This is not something I think of on a daily basis."
Zverev wasn't the lone big name to be stretched in the men's bottom half, with Grigor Dimitrov -- who won the year-end championships in 2017 -- and 2014 US Open finalist Kei Nishikori also overturning 2-1 set deficits.
Dimitrov got past American Jared Donaldson 6-7 (4-7) 6-4 4-6 6-4 10-8 in four hours, 19 minutes and Nishikori improved to a phenomenal 120-38 in deciding third or fifth sets when the Japanese beat the always unpredictable Benoit Paire of France 6-3 2-6 4-6 6-2 6-3 in three hours.
Unable to serve properly as he appeared to suffer from a leg cramp of his own, Donaldson -- fined after famously clashing with a chair umpire in Monte Carlo in April -- resorted to an underhand serve at 6-6 in the fifth.
The crowd didn't approve but the 21-year-old won the point as the Bulgarian sent his return long. He did it again at 8-8 but lost the point.
Dimitrov wasn't fussed.
"I think it's great and it's in the game," said Dimitrov, who suspected he did it once in his career. "Simple as that. I know why he did it. He was hurting big time."
Dominic Thiem -- arguably the leading contender to make the final from the bottom half -- led Greece's Stefanos Tsitsipas 6-2 2-6 6-4 in an entertaining battle on the new court 18 when darkness halted play. In the most recent of their three duels in April in Barcelona, the 19-year-old Tsitsipas triumphed over the world No. 8.
The last women's player to start her first-round match -- rain contributed to that -- was world No. 1 Simona Halep and the Romanian recovered from a slow start to dispatch another American, Alison Riske, 2-6 6-1 6-1 to start play on the main Philippe-Chatrier court.
She admitted to having nerves despite her lofty ranking.
"I'm a normal person, even if I am No. 1 in the world," said Halep, popular in part due to her honesty.
Won set off Nadal
Zverev's star shone even brighter in the buildup to the French Open when he won the title in Madrid and led Nadal by a break in the final set of the Rome finale. A rain delay ultimately swung the momentum in the Spaniard's favor.
Nadal said afterward he was sure Zverev -- mentored by six-time grand slam winner Boris Becker -- would indeed experience success at grand slams soon but Lajovic initially did not read the script.
Striking his one-handed backhand with venom and throwing in his share of drop shots, the Serb stormed to the first set. In similar style, he upset Juan Martin del Potro in Madrid for a first top-10 win.
Lajovic may feel the second set was the turning point: He broke early but failed to hang on to the lead.
Lajovic did recover in the third and as Zverev's frustration grew, he slammed his racket onto the red clay.
Zverev's past foibles in grand slams however didn't phase him -- he was still competing well. And once he secured a double break advantage for 5-1 in the fourth, the job was almost done.
Zverev began hitting with more authority, though was aided by Lajovic's physical duress.
"In the fourth and fifth set I really felt good out there even though I was a little bit tired and a little bit fatigued," said Zverev, whose next opponent, 26th seed Damir Dzumhur, also went to five sets Wednesday.
Marco Trungelliti's adventure
, meanwhile, ended as the Argentine succumbed to Italy's Marco Cecchinato 6-1 7-6 (7-1) 6-1.
Slow starts for Halep
When Riske -- a finalist on clay Saturday in Nurnberg to return to the top 100 -- took the opener it marked more struggles for Halep early in majors.
She trailed Destanee Aiava 5-2 in the first set of her first match in Melbourne and saved three match points in the third round against Lauren Davis.
Halep went on to make the final, narrowly losing to Caroline Wozniacki.
Still seeking a maiden grand slam title, Halep has lost two heartbreaking finals at the French Open, too, to Maria Sharapova in 2014 and Jelena Ostapenko last year.
Two other women's contenders, Petra Kvitova and Elina Svitolina, advanced in straight sets against Lara Arruabarrena (6-0 6-4) and Viktoria Kuzmova (6-3 6-4).