Blackburn Rovers have signed midfielder Jay Spearing from Bolton on loan until the end of the season
Rotherham have brought in Crystal Palace defender Jack Hunt on loan until the end of the season.
Mata became the first Blues player to react publicly to the sacking of Roberto Di Matteo and he has now led the way in responding to the controversial decision to hand former Liverpool boss Benitez the reins until the end of the season.
He told the Daily Mail: "Rafa Benitez is a great coach.
"He's got lots of experience and won a lot of trophies with Liverpool, taking them to a very high level. He knows the Premier League too."
Benitez's appointment has been seen by some as owner Roman Abramovich's latest attempt to get £50million flop Fernando Torres scoring.
Torres has never recaptured the form he showed under Benitez at Anfield but Mata said: "I have total faith in Fernando Torres. He will score goals. He is a great striker and a great professional."
Di Matteo was sacked after Chelsea's 3-0 Champions League defeat at Juventus, in which he dropped Torres for the first time.
Mata added: "Di Matteo's sacking means things haven't been going well but we can't just blame it all on the Juventus game.
"We can't just focus on what happened recently.
"It was a really tough blow losing to Juventus. It was a sad night for all the players. We thought we could at least draw, if not win the game."
Mata took to social media on Wednesday to wish Di Matteo well after Abramovich ruthlessly dispensed with the Italian only hours after the defeat in Turin.
He posted on Facebook: "would like to thank him for all this time with us and wish him the best of luck for the future.
"As a player, he has been a legend for the 'Blues'.
"With him as a manager, we won our first Champions League. He will always be remembered. Good luck Robbie!"