The Euroclay season ended with a resounding bang Sunday in Rome, where Alexander Zverev upended Novak Djokovic to win the Rome Masters 1000. The upset followed just hours after Elina Svitolina pulled off a similar feat, defeating Simona Halep in the WTA final at the same event.

Those surprising results were in keeping with many of the other events that occurred during the 15 clay-court events, including three ATP Masters 1000s and three WTA Premier-level events.

Here are some of the takeaways leading up to the French Open, which starts Sunday in Paris:

The future of the ATP has arrived

Alexander Zverev beat Rafael Nadal en route to this biggest tournament win of his career, at the Rome Masters. Sport Tennis

Rafael Nadal did yeoman work keeping the Big Four -- the old guard of tennis -- well-represented on the Euroclay circuit. But make no mistake, the young challengers are stirring. Zverev, who's 20, validated all the hype that has trailed him by becoming the youngest winner at a Masters 1000 since Djokovic won the 2007 Miami Open. Zverev enters the French Open fresh off his biggest win of his career, a straight-sets win against Djokovic. Zverev will be ranked No. 10, up six spots, when the event begins.

Dominic Thiem was a finalist and semifinalist, respectively, in the Madrid and Rome Masters. He lost the Madrid final to Nadal but beat him in the Rome quarters -- the only player to claim a W over Nadal on clay this year.

Borna Coric, Hyeon Chung and Karen Khachanov also made great strides. Nick Kyrgios played just one Euroclay event because of a hip injury that threatens his chances in Paris. But the message is clear: Seeds in Paris beware.

Rafael Nadal is the man to beat in Paris

Despite coming up short in Rome, Rafael Nadal still won three clay events leading up to the French Open. REUTERS/Sergio Perez/File Photo

As the tour moved to clay in Europe, all eyes were on Nadal. After a great start, could he complete his resurgence by re-establishing his dominance on clay? Yes. Not only was Nadal technically and tactically sound as ever, there was no sign of the self-doubt and hesitation that poisoned his game in the long slump that dated back to 2014.

Nadal is a tour-leading 36-6 with three titles. He had convincing wins over Djokovic, Thiem, Goffin, Kyrgios and even former nemesis Fabio Fognini during the Euroclay season. Thus Nadal will be the odds-on favorite to win in Paris.

Big question marks for the WTA

World No. 1 Angelique Kerber has not won a tournament this season. Julian Finney/Getty Images

Serena Williams is out on maternity leave. No. 1 Angelique Kerber hasn't won a tournament this season and her record is only 19-12. The much-anticipated return of Maria Sharapova from her suspension was not to be after the French Tennis Federation denied her a wild card in the main draw and qualifying.

Neither multi-time Grand Slam champs Victoria Azarenka or Petra Kvitova will be in the draw, either, though the former hopes to be playing a few weeks later at Wimbledon.

There will also be question marks regarding defending champ Garbine Muguruza, who retired from her semifinal match in Rome with a neck injury.

But the absences will open up an opportunity for another player. Perhaps Rome champ Svitolina or runner-up Halep, whom we've expected to make a breakthrough on clay for some time, will make a deep run. We can only wonder at this point.

Novak Djokovic's French Open chances: slim to none

Novak Djokovic will enter the French Open with a new mentor, Andre Agassi, by his side. Fabio Averna/Getty Images

In announcing after the Rome final that he will be working with Andre Agassi in the future, Djokovic implied that there will be more meeting and talking than coaching when the two get together in Paris. In fact, Agassi has already told Djokovic that whatever happens, the former American star won't be able to stay in Paris for the duration of the event.

Djokovic is in the midst of a major transition. He hasn't slumped far, but it's far enough to make him vulnerable. Of greater potential impact, his motivation seems crippled. He looked like the dominant Djokovic of yore when he crushed Thiem in the Rome semis but couldn't muster the resistance the following day to claw his way to a single break point in the final against Zverev. That kind of inconsistency won't fly in Paris.