Serena Williams' former coach, Patrick Mouratoglou, is seeing another "Big 3" forming up in the tennis world with Ben Shelton, Carlos Alcaraz and Jannik Sinner, poised to replace the legendary trio of Roger Federer, Rafael Nadal and Novak Djokovic.While Alcaraz and Sinner have already made big strides in their tennis careers by winning five and four Grand Slams, respectively, Shelton still hasn't won a Grand Slam. However, he's getting nearer after winning the ATP Masters event at the Canadian Open.Mouratoglou compared Shelton to Djokovic, saying just like the Serbian, who once came knocking to shake down the domination of Federer and Nadal, Shelton might very well do the same. He thinks that now that Shelton has won a Masters 1000 event, he will be high on confidence entering the US Open."For Ben Shelton, winning a Masters 1000 is huge," Mouratoglou said. "This is the last stage before winning a Grand Slam, so it's big. Can he challenge Alcaraz and Sinner? Yes and no. Today, it's difficult to imagine, because those guys are really playing incredible tennis, but Ben has things that the others don't."Williams' former coach highlighted what makes Shelton special and different from others. He added:"He has this incredible serve. Second, he's a lefty, which is a big advantage too. And I would say third, he's really unpredictable. Most importantly, he has belief. This reminds me of Novak when Rafa and Roger were winning everything. Young Novak said, 'I'm gonna beat those guys.' Ben thinks the same." View this post on Instagram Instagram PostShelton is coming off a loss in the quarterfinal of the Cincinnati Masters against Alexander Zverev, 6-2, 6-2. He'll now prepare for the US Open mixed doubles where he's set to pair up with Taylor Townsend.Ben Shelton sets his sights on the US Open after Canadian Open breakthroughEarlier this month, Ben Shelton captured his first ATP Masters 1000 title at the Canadian Open in Toronto. He rallied past Karen Khachanov in a tense final, claiming the trophy with a 6-7(5), 6-4, 7-6(7-3) victory.With that, he became the youngest American to win a Masters 1000 hard-court event since Andy Roddick in 2004. While Shelton has his sights set on winning a Grand Slam, he isn't taking the bait of falling prey to massive expectations.“I don’t really feel expectations other than what me and my team put on myself, which is more about effort and intention than results,” he said. “That’s always kind of how I go into a tournament. Whatever happens, happens."I know that the way I play, I have big weeks. I also know that there’s a lot of great players on tour and any given day, you can get upset or beat. So I don’t think about expectations that much. I just think about my goals in terms of where I want to see my game.”On any given day, anything can happen on a tennis court. However, Ben Shelton isn't thinking too much ahead of himself as he still has a lot to do to win best-of-five games against top players such as Sinner and Alcaraz in Grand Slam matches.