The Blues captain says the Portuguese has boosted the squad's waning winning mentality, with the side third in the Premier League and just two points off the top
The Portuguese left Stamford Bridge in September 2007 after winning two Premier League titles and three domestic cups in his three full seasons at the club.
After coming back in July, the Blues have won twelve of their opening 19 games and lie just two points behind table-toppers Arsenal.
Consequently, Terry believes the club has its mojo back.
"The last couple of years we've lost our identity a little bit," the veteran centre-half told the club's official website.
"There's some good teams in the league and when you go 3-2 up it's important you get men behind the ball and dig in deep and not give them opportunities to really feed on.
"I think we're doing that really well at the moment. At times when we're looking really solid, getting the wide men in and then when we do break it's important for them to then go again and show their fresh legs going forward."
Chelsea are unbeaten in their last four league games, beating fellow title challengers Liverpool 2-1 last time out thanks to strikes from Samuel Eto’o and Eden Hazard.
And Terry says those type of attacking players are key for the side’s silverware ambitions.
"It's important you keep it tight at the back and you look for those type of players to create something or do something out of nothing," the Blues captain added.
"He's been doing that all season [and] scoring. The last four or five games he's been really tracking back and really dug in. He's really dug in and added that to his game and made him the complete player."