US player Serena Williams celebrates with the winner's trophy, the Venus Rosewater Dish, after her women's singles final victory over Spain's Garbine Muguruza on day twelve of the 2015 Wimbledon Championships in southwest London, on July 11, 2015US player Serena Williams celebrates with the winner's trophy, the Venus Rosewater Dish, after her women's singles final victory over Spain's Garbine Muguruza on day twelve of the 2015 Wimbledon Championships in southwest London, on July 11, 2015 (AFP Photo/Leon Neal)
Williams became the oldest woman to win a Grand Slam title as she secured her second "Serena Slam" of holding all four majors at the same time and now just needs to defend her US Open trophy in September to complete a rare calendar Grand Slam.
"Serena is unique. There is only one Serena," said the French coach.
"In terms of level, she played great tennis. At Roland Garros she was so sick but she managed to lift her level really high at this Wimbledon.
"To win four Grand Slams in a row is an incredible achievement. Winning just one Grand Slam for anyone is such a big achievement.
"Here she had such a tough draw, playing Heather Watson, Venus, Vika (Azarenka) and Sharapova. The draw was so difficult, she had so many tough matches, but she made it every single time against every kind of adversity.
"She faced different game plans, different kinds of tennis, being sick, not feeling great every day.
"It's incredible to be able to focus and show so much dedication and ability to turn things around when you are in trouble."
The 45-year-old Mouratoglou said Serena's slow start on Saturday, when she served up three double faults to drop serve in her opening game, was down to the nerves of the occasion as she closed in on another Grand Slam title.
"It was more an emotional match today because it was the final. The emotion was too high at the start and at the end. It was a different kind of adversity," he said.
- Calendar Slam -
Mouratoglou said that Williams will not be fazed by the pressure of trying to secure the first calendar Grand Slam since Steffi Graf in 1988 on home ground in New York.
"Every Grand Slam event is enough of a motivation for her to be at the top of her game. The motivation is always the same," he added.
The coach also warned the likes of Sharapova, Petra Kvitova, Azarenka and the host of players hoping to dethrone the American that Williams is simply a class above them.
"When she plays her best, she is better than anyone," he said before offering a crumb of comfort, "but she doesn't play her best every day."
Williams's win on Saturday, which put her one Grand Slam title behind Graf's Open Era record of 22, will rekindle the debate over her place in the pantheon of the sport's greatest ever.
"We can talk about history when she stops playing, she is still playing so the best answer is out on the court," added Mouratoglou.
"My goal is that she gives the best answer with her racquet."
He added: "There will be pressure in New York. But it was already super-high here.
"Journalists were talking to her about the Serena Slam every day here. She managed to do it. I'm not worried about her."