Carlos Alcaraz keeping tabs on 6ft 8 tennis giant whose 149mph serve shocked Ben Shelton

revealed that he'd been keeping tabs on one of his emerging rivals.

Giovanni Mpetshi Perricard lifted his second title and his first at ATP 500 level on Sunday, beating to win the Swiss Indoors Basel.

Alcaraz beat the young Frenchman en route to his recent China Open title. And the world No. 2 admitted he'd been checking Mpetshi Perricard's serving stats during Sunday's final.

Mpetshi Perricard started the year ranked outside the world's top 200 and now sits at a career-high of No. 31 following his triumph in Basel. The 21-year-old stands at 6ft 8", with his height giving him a major advantage on serve.

One of his fastest serves of the final clocked in at 149.8mph - and Shelton somehow managed to hit a return winner off of it. Even his second serves were bullets, with Mpetshi Perricard firing down a 146mph belter.

His performance is Basel sent a statement to the rest of the tour and Alcaraz took note. The Spaniard beat the 21-year-old in his opening match at the Beijing Open, a tournament he went on to win.

Although he came out on top, Alcaraz is well aware that Mpetshi Perricard could soon pose a big threat. Asked if the French star had the best serve on tour, the world No. 2 replied: "Without [a] doubt. Yeah, I mean, the way he serves is unbelievable."

The four-time Grand Slam champion knew his stuff, revealing that he kept an eye on the numbers in the championship match. "I saw the stats in the final. The average of the first serve, it was 235 [km/h], and the second serve it was 215. So that's the average," Alcaraz smiled.

"That's crazy. Yeah, I played against him recently, was totally different conditions. Obviously the court was slower, so I could return his serves few times, you know, in the games that I broke his serve.

"So it was difficult, because, you know, from the baseline he has big shots, as well. Really good forehand, good volleys. You know, he can be solid from the baseline. So I think he just have to win in Basel and probably is a player who is going to be there for a long time."

Shelton's serve is also known for being a huge weapon. But

"I want to congratulate Gio on a great week and a great match today," he said in his runner-up speech.

"I almost killed myself trying to return your serve. So many other parts of your game have improved so much and you're such a great young talent and so good for the sport."