Tendulkar achieved the milestone on Sunday as he battled to save the first Test against South Africa in Centurion.
It was a remarkable achievement for Tendulkar in his 175th Test, but it came as little surprise to Kirsten.
Kirsten said: "Every innings he's very determined to go out and do something. This is an incredible individual milestone but he's really focused on making big contributions for the team.
"He wants to make his runs in important situations. He wants to make sure the team's doing well whilst he's getting those individual milestones.
"He's enjoying his cricket more than he ever has. For the team having done well over the last couple of years has given him a new motivation to make his runs and make his contributions for the good of the team.
"He's just got better and better. This year he's been unbelievable.
"For me he's a professor in batting. He's very streetwise in terms of the way he goes about his business.
"He understands every situation that he's confronted with in a match and he plays accordingly."
Tendulkar (107 not out) and Mahendra Singh Dhoni (90) shared a 172-run seventh-wicket stand, but India closed day four when a storm blew in on 454 for eight, still 30 runs short of making South Africa bat again.
Kirsten cited Tendulkar as an example for all aspiring players to follow, saying: "He still works extremely hard on his game. I think I throw more balls in the nets to him than anyone else.
"It's little wonder that he's been so successful over so many years because he treats every cricketing day with humility and respect and works as hard as he can on his game.
"He just loves the game. He wants to be out there, he wants to hit balls, he wants to practise - but I think it's the way he practises which is the key.
"It's a great lesson for young cricketers.
"He doesn't take one ball for granted in a practice session. He tries to hit it perfectly every time and you'll never see him having a loose net, or playing a loose shot. He gets very irritated when he gets out."
Tendulkar has scored seven Test centuries in 2010, the most he has ever managed in a calendar year.
Kirsten said: "He studies the whole book for the exam then goes out and gives himself the best chance for success."
