The two managers come face to face in Wednesday's crunch Champions League clash at the Mestalla.
Villas-Boas will put his friendship with Emery to one side for the Blues' second Group E game in Spain - a match that is beginning to look by far their toughest en route to the knockout stage.
Like 33-year-old Villas-Boas, Emery began his managerial career in his early 30s, and the pair are now considered two of the brightest young coaches around.
After injury forced him to hang up his boots, Emery enjoyed instant success at both Lorca and Almeria before being tasked with reviving debt-ridden Valencia's fortunes just over three years ago.
Despite being forced to sell star men such as David Villa, David Silva and - most recently to Chelsea - Juan Mata, the 39-year-old has done just that.
They have twice finished third behind the mega-rich Barcelona and Real Madrid and stormed to the top of the Primera Division this season before Wednesday night's 2-2 draw with the former, who they were 13 minutes away from beating in a thrilling contest.
"Unai is a very, very good coach," said Villas-Boas, who was otherwise occupied on Wednesday as Chelsea were beating Fulham in the Carling Cup but had a scout at the Mestalla.
"I think he can be one of the future greatest managers.
"He organises his teams very well and all of what he has done in his career is down to his attitude towards the game and the way his team plays.
"He is a friend of mine and I'm happy he is doing well."
Despite their fine start domestically, Valencia failed to kick off their Champions League campaign with a victory, having been held to a goalless draw at Genk a week and a half ago.
"The result at Genk was unexpected," said Villas-Boas, whose Chelsea side beat Bayer Leverkusen on the same night to take the early initiative in Group E.
"Genk is a difficult place to go and it's a very tight stadium with a good environment.
"But I was expecting Valencia to take the win.
"So I would say that this is a game where Valencia will try to get three points.
"A win at Valencia would put us in a very, very good position."
After playing for more than 70 minutes with 10 men in Wednesday night's Carling Cup penalty shootout win following Alex's red card, Villas-Boas made wholesale changes to his side for today's Barclays Premier League game against Swansea.
But he revealed that would not have a knock-on effect for the Valencia game, insisting it was too early in the season to worry about burnout.
"You don't know how many games you're going to play during the season, so we just have to wait and see," he said.
"We hope to progress to a good season but, at the moment, I would never take that into account.
"Players can be overloaded - I agree - but due to the different international appointments they have and the games they play for their teams."
That is likely to mean an early reunion for Mata and his former Valencia team-mates, while Oriol Romeu is also set for a quick return to Spain after quitting Barcelona this summer.
The holding midfielder, who turned 20 today, impressed during his full debut on Wednesday.
"You saw the potential of the player," Villas-Boas said.
"He's competing with (John Obi) Mikel and Raul (Meireles) in that position and he played to a good level.
"All of them have the talent to play in that position.
"They have, of course, their individual characteristics and we try to promote what is their individual talent.
"All of the three are very, very good."
Source: Team Talk
Source: Team Talk