Marcos Alonso's goal was his fourth in the Premier League this season
The Blues' 1-1 draw with Leicester puts them three points clear of Tottenham, in fourth, with a game to go.
Chelsea have a superior goal difference of 18 over Spurs.
Kante has missed more than half the season with various injuries and Tuchel said: "He is the guy who makes the difference."
The German added: "I think he is our key, key, key player; but key, key, key players need to be on the pitch.
"He plays only 40% of the games. So it's maybe a miracle that we arrived in third place.
"Because he is our Mo Salah, he is our [Virgil] Van Dijk, he is our [Kevin] De Bruyne, he is simply that player. He is our Neymar, he is our Kylian Mbappe."
Chelsea, beaten in the FA Cup final by Liverpool at the weekend, fell behind early on at Stamford Bridge when James Maddison curled a fine effort beyond goalkeeper Edouard Mendy.
However, Marcos Alonso equalised towards the end of the first half when he was picked out superbly by Reece James and volleyed in.
Chelsea dominated the second half and had numerous chances to take all three points.
Hakim Ziyech went close with a free kick while Romelu Lukaku - who had been largely quiet - headed wide.
But Christian Pulisic failed to convert the best chance for a winner when he sliced wide from eight yards with the goal at his mercy.
The result means Chelsea stay third, three points ahead of Tottenham, but with a vastly superior goal difference.
Tuchel's side finish the season at home to relegated Watford on Sunday (16:00 BST) while Leicester, who are ninth, will look cement a top-10 finish when they host Southampton at the same time.
Any jeopardy for Chelsea in this game disappeared on Monday, when their place in the top four was confirmed by Arsenal's defeat at Newcastle.
But with back-to-back home fixtures to finish the campaign, the Blues had a chance to end on a high before switching focus to the future - and the pressing issue of getting the club's ownership sorted.
Initially, Chelsea were sluggish, a possible hangover from their FA Cup loss, but they improved as the game wore on and were unfortunate not to take all three points.
That they didn't win was down to their inability to finish chances, a problem that has plagued them this season.
Maddison, named Leicester's player of the season earlier this week, is enjoying his best Premier League goal return in a season, taking his tally to 11 with his striker at Stamford Bridge.
The midfielder had a spell out of the team in the early months of the campaign when he admitted he was struggling for confidence but has not looked back since returning.
In total, he has scored 17 goals in all competitions, chipping in with 11 assists, which surely will not have gone unnoticed by England boss Gareth Southgate as he plans his squad for the World Cup in Qatar later this year.
-- Courtesy of BBC Sport