The Belgium midfielder scored the game’s only goal when he let fly from 25 yards in the 63rd minute in front of 21,000 fans at Wembley.
Tielemans became the first Leicester player to score in an FA Cup final since Ken Keyworth in 1963 as he ended the club’s FA Cup final hoodoo.
It was then Leicester captain Kasper Schmeichel’s turn to be the hero when he denied Ben Chilwell and Mason Mount with two outstanding saves late on.
There was late drama, though, as Chilwell, who left Leicester to join Chelsea last summer, thought he had equalised for the Blues in the 89th minute.
However, VAR ruled the goal out for the tightest of offside calls.
The Foxes had come unstuck in four previous FA Cup finals, but finally put that unwanted record to bed.