Andre Agassi will be in Novak Djokovic’s box when he begins the defence of his French Open title next week – at least for a few matches.

However, the world No2 left Rome on Sunday spiritually bruised and a little bewildered after losing in two one-sided sets to the 20-year-old Alexander Zverev, who shows all the promise the Serb displayed as a teenager a decade ago. This was a performance and a result to announce the arrival of a new prince in the game.

The Italian Open final, which Djokovic has won four times, was his last match as a 29-year-old, and was a wretched denouement to a fine week of recovery for him. As he celebrates his birthday on Monday, he will want to quickly forget the dominance of the German with the flowing locks, booming serve and a backhand that ground his opponent into the Roman clay over an hour and 21 minutes, winning 6-4, 6-3. Perhaps Agassi can offer the balm he needs.

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Djokovic said later: “I spoke to Andre the last couple weeks on the phone, and we decided to get together in Paris. We don’t have any long-term commitment, it’s just us trying to get to know each other a little bit. He will not stay the whole tournament. He’s going to stay only to a certain time, and then we’ll see after that what’s going to happen.”

The odds are Agassi, who values his home life, will stay briefly. It is almost certain he will not last as long as Boris Becker, whose three-year stint ended in December. But Djokovic says he and the American are a good fit. He sounds, even, as if he’s looking for a life coach.

“Andre is someone that I have tremendous respect for as a person and as a player. He has been through everything that I’m going through,” Djokovic said. “He understands the game amazingly well. I am enjoying every conversation that I have with him. Also, he’s someone that nurtures family values, philanthropic work. He’s a very humble man, very educated. He’s a person that can contribute to my life on and off the court a lot. I’m very excited to see what is ahead of us.”

If Zverev really is the new prince of tennis, he is a gloriously photogenic one – and that alone will bring unfamiliar, but perhaps not altogether unwelcome, stress when he arrives in Paris this week as the latest conqueror of one of the Big Four.

Zverev is the fresh face of what is becoming firmly established as the Next Generation. His victory against Djokovic to win a Masters 1000 title at the first attempt was, beyond debate, stunning. He shocked the Serb. He delighted the patrons. And he gave every player at or around his age the sort of encouragement that inspires great deeds.

The timing was perfect for Zverev, appalling for Djokovic. The French Open was the Serb’s last major title. Since then he has lost his mojo, his world No1 ranking to Andy Murray and some of his self-belief. Last week he shocked all but those close to him when he parted with the coaching staff who had been with him since he won the first of his 31 Masters titles, in Miami when he was 19. Now he has Agassi for company, at least for a week or so.

Zverev, the youngest Masters champion since Djokovic, battered the best returner in the game with seven aces, pinned him deep with raking groundstrokes to both corners and not for a moment did he look as if this significant upset was anything other than what he had expected. He won as he pleased, hard as that might be to imagine.

Djokovic said of Zverev, who moves into the top 10 on Monday: “He’s making his mark already. He played great, served great. His backhand was very fast and solid, not many errors at all and a big serve. It was a perfect performance. I played very poor today.”

He blamed the wind and the bounce. The real reason stood 6ft 6in at the other end of the court. In the stands three grand old champions, Rod Laver, Manuel Santana and Nicola Pietrangeli, turned to each other occasionally, murmuring. They might have been reaching back in time to their own youth, when the Roman sun beat as hard but the ball rarely flew as fast as this.

Around this magnificent packed amphitheatre, as the shadows crept across the clay, others wondered, too, if they were witnessing the beginning of a wonderful journey. John Isner, whose long legs gave up on him at the end of their absorbing three-setter the day before, said Zverev, whom he knows well, had what it takes to be “one of the greats”. Jez Green, his conditioner, is in awe of his physical prowess, a tall powerhouse who moves like someone who matches the game’s beau ideal closer to 6ft – like, well, Djokovic. The player he most reminds Green of, though, is Marat Safin. “Today was one of the best matches I ever played,” Zverev agreed. “I knew I had to be aggressive from the first point to the last.

“At the net he wished me all the best for the future and for Paris. He knows me since I’m four years old. My brother [Mischa] and him are the same age. They have been playing since juniors together. I always practised with him. He always took me for warm-ups when I was still a junior and stuff like this at big tournaments and grand slams. He’s one of the best guys on tour. Unfortunately for tennis and unfortunately for the spectators, the top four cannot play forever.”

All week he had avoided speculating about his chances of winning this tournament. Now, though, he can dream a little bigger. “To win the French Open? Before this week I would have given myself close to zero chances of winning here. But as I showed this week, I can play and beat the best players at the biggest tournaments. Hopefully I can continue my form into Paris ... and we’ll see what it holds for me there.”

It would be extraordinary if he were to replicate his Italian success at the French, especially as Rafael Nadal has hit such a rich vein of form on his favourite surface. The pressure and angst that comes with winning the best of five sets is also something he has yet to experience. He should not lumber himself with expectations that might drain him of the joy he brings to the court.

That is his secret: an unfettered love of hitting the ball hard and with total conviction. As Isner said, Zverev has “swagger”. He will need it, because those among his contemporaries who might regard themselves as serious contenders for Djokovic’s title do not lack for the quality – Dominic Thiem, who beat Nadal, for instance. Djokovic blew him away in conditions which suited him but he could not do the same to Zverev in the swirling breeze that swept Campo Centrale on Sunday.

The last four shots Djokovic played described his sorry afternoon: a ragged, desperate forehand from outside the lines for deuce, another that clipped the net and went out, a double fault for match point and a final weary backhand long.

Zverev, who some say knows his worth better than others, went to his bench, put his head in his hands and sobbed. It was as it should be.

Earlier Simona Halep turned her right ankle at 5-2 in the first set – and later complained of a left thigh strain – neither of which setback helped her mood or her ability to lift a poor final out of the mire as the eighth seed, Elina Svitolina, eked out a 4-6, 7-5, 6-1 win in just over two hours.