Coach Rick Macci reveals astonishing strength Maria Sharapova had already at 11

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Coach Rick Macci says Maria Sharapova "had that mental box at 11 already" and that's something he didn't even see in Serena Williams. Macci, who famously worked with several all-time greats in their childhood, had a chance to take a look at Sharapova and Williams even way before they became global tennis stars.

According to Macci, Williams was checking every box game and technically-wise. When it comes to Sharapova, Macci felt she was lacking in the athletic aspect but her mental strength was astonishing.

Macci: Sharapova had that mental box at 11 already, I didn't see it in Williams

"You’ve got to remember to forget.

You got to have the ability to forget. In tennis, it’s very tricky and this separates great from good. You know great is rare air. There’s a lot of good athletes, amazing athletes on the WTA and ATP tour but they’re not the leaders of the clubhouse.

They didn’t become a [Rafael] Nadal… I know it’s a package – the forehand, backhand, serve – you have got to check a lot of boxes. Serena checked every box and created a few more but you have got to check every box.

But the mental part -- how you handle pressure… and the ability to forget. You have got 20 seconds to flip it in your mind like it happened 20 years ago. That’s why I love Sharapova… even at 11, she was in a bubble.

I called it. Even though she was limited athletically, she had that mental box already there. It was amazing. I didn’t see it in Serena," Macci said on the ATP Tennis Radio Podcast.

Both Sharapova and Williams went on to achieve great success early.

In 1999, Williams became a Grand Slam champion at the age of 19 after winning the US Open. Five years later, a 17-year-old Sharapova won Wimbledon. In the end, Williams won 23 Grand Slams while Sharapova finished with five Slams.