The sixth seed is fast becoming one of the best players on the ATP Tour, but he was superb in surging to a 7-6 6-3 6-0 victory over the former world number one.
There will be questions over the performance of Djokovic, who became increasingly wayward as the match progressed, but Thiem deserves the plaudits for reaching the last four at Roland Garros for the second consecutive year.
The opening set was fiercely contested with four breaks of serve being shared between the two players, but it was Thiem who held the edge in the tie-break and eventually claimed it by a 7-5 scoreline.
A response was expected of Djokovic but he was unable to find his range as Thiem continued to play with confidence, and one break was enough for the Austrian to move closer to the semi-finals.
Djokovic was becoming increasingly out of sorts and in a set where he won just eight points and committed 12 unforced errors, Thiem inflicted a bagel on the defending champion in just 20 minutes.