Williams sought out the French coach, who runs an academy in Paris, following her first-round loss at the French Open last season and since then has been virtually unbeatable.
The American has won 16 singles titles in the last 16 months, including four grand slams and an Olympic gold medal, while this season she has lost just four of her 82 matches.
At 32, Williams is further ahead of the pack than she has ever been and on Sunday she finished off the year with another piece of silverware as she successfully defended her WTA Championships title in Istanbul.
The only year to compare to this one was 2002, when Williams won three successive grand slam trophies before going on to complete the 'Serena Slam' at the 2003 Australian Open.
The only real disappointments for Williams this year have been her losses at the Australian Open and Wimbledon, and she has been reluctant to label the season her best.
Mouratoglou said: "I don't know how important it is to say it's her best. In many aspects, the numbers, it is the best by far. But she won only two grand slams. It's good because in 2014 we can do better.
"The most satisfying thing is the consistency. In 90 per cent of her matches she had the consistency from the start to the end. That is the main thing that I think is new, she's never showed that throughout the year and I think it made her improve a lot.
"She's used to playing half less matches with half less focus, so you can imagine the effort it took her to achieve it this year."
Sheer force of will played a significant part in an exhausted Williams' final victory over Li Na on Sunday.
The Chinese player easily won the first set but Williams changed the momentum at the start of the second and ran away with the third to win 2-6 6-3 6-0.
"It would have been very disappointing to lose with the season that she had," said Mouratoglou.
"Winning that match is fitting. Obviously she was really tired. She started the tournament really well but the more the tournament went on, the more tired she was getting.
"The last two matches were really tough, and we have to say that Li Na played some of the best tennis of her life so the combination of the two made the first set and the start of the second a bit dangerous.
"I think the first game of the second set was really a key moment of the match. She found a way to win her serve facing break points. I think also she understood that she was making some tactical errors, she was opening the court too early.
"But she stayed calm and she managed to switch the match in her favour. When you feel the way she feels at the moment and the opponent is playing at that level, to find a way to change the match you really have to believe and refuse to lose.
"That's something that she really has and it makes a difference between her and most of the players."
Williams will undoubtedly be the favourite to win the Australian Open when the new season kicks off in January, but for now she will turn her focus to rest and recovery.
Mouratoglou added: "The best thing she can do now is to switch off a little bit.
"During the (trophy) ceremony we were talking and she said, 'There's a few things I need to talk to you about that I think I have to work on'. She will keep in mind the things that didn't work - and I think she's right."