(CNN) 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."
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 Rafael 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.
Photos: French Open 2018: Title No. 11 for Rafa? Serena Williams turned heads in this black catsuit as she made her first grand slam appearance for 16 months following the birth of her daughter in September. The 23-time grand slam champion said it made her feel like a "warrior princess" but added it helped with her poor circulation. Hide Caption 1 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Rafael Nadal is back in Paris and bidding to stretch his record to 11 French Open titles after beating Stan Wawrinka in last year's final at Roland Garros. Hide Caption 2 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Spain's Nadal is known as the "King of Clay" and is the red-hot favorite in Paris. Hide Caption 3 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Last year about 15,000 people packed into Roland Garros' Philippe-Chatrier court to watch Nadal make history as the only player in the modern era to win the same grand slam 10 times. Hide Caption 4 of 13 Photos: French Open 2018: Title No. 11 for Rafa? The French Open oozes Parisian chic and is a springtime rite in the capital. Hide Caption 5 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Novak Djokovic's recent results suggest the 12-time grand slam champion could be turning the corner in his recent struggles. A win on day two was a decent start for the 2016 champion, who has slipped to 22 in the world. Hide Caption 6 of 13 Photos: French Open 2018: Title No. 11 for Rafa? A year on from her return from a knife attack in her own home, Petra Kvitova tells CNN she is living "a dream." The Czech star, a two-time Wimbledon champion, has yet to reach the final in Paris but escapes on day two after losing the first set. Hide Caption 7 of 13 Photos: French Open 2018: Title No. 11 for Rafa? On day one in 2018, defending champion Jelena Ostapenko was dethroned by Kateryna Kozlova. Hide Caption 8 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Bad news travels in two as Venus Williams also suffered a shock exit after losing to Wang Qiang. Hide Caption 9 of 13 Photos: French Open 2018: Title No. 11 for Rafa? No Frenchman has triumphed on home clay since Yannick Noah in 1983. Hide Caption 10 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Famous faces are fixtures in the stands at Roland Garros. Last year actress Nicole Kidman took in the men's final. Hide Caption 11 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Maybe some of those famous faces watched Serena Williams on Tuesday. Williams won as she returned to grand slams after becoming a mum last year. Hide Caption 12 of 13 Photos: French Open 2018: Title No. 11 for Rafa? Maria Sharapova also made her return to Roland Garros on the third day after a drug ban in 2016 and not receiving a wildcard last year. Hide Caption 13 of 13
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.
Lajovic's countryman Novak Djokovic had a quicker tussle but that didn't mean it was easy for the 12-time grand slam winner. Far from it.
He was pushed all the way by Spanish qualifier Jaume Munar -- mentored by Nadal, his fellow Mallorcan -- before advancing 7-6 (7-1) 6-4 6-4.
The result continued Djokovic's renaissance following elbow surgery that dovetailed with a loss of motivation.
"At times I do lose maybe a comfort level on the court and confidence, and that's something that I'm still building gradually, obviously," said the 2016 winner. "The more matches I play, the better it is. The more I win, of course, the better it is."
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.
"I think the nerves are really good. It means that you care about what you are doing and your desire is really big.
Every time when I get on court is like I'm really excited and nervous about everything, every moment."
- @Simona_Halep #RG18 pic.twitter.com/NgAN7XrG3y — Roland-Garros (@rolandgarros) May 30, 2018
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).