The Serbian has not featured on Tour since the 2013 Croatia Open having failed to supply a blood sample at the Monte Carlo Masters earlier in the same year, but he showed no signs of rustiness with a 7-6 (7-4) 6-4 win over the eighth seed.
Troicki showed the qualities that had seen him reach number 12 in the world as he set up a second-round match with Andrey Golubev.
His victory could have been even easier at the ATP 250 clay-court event had he not thrown away a 5-4 lead and three set points in the opening set, however he won four points in a row in the tie-break to take the lead.
When the 28-year-old managed to get his first serve in he won 73 per cent of the points and also targeted the second serve of Thiem, winning points on 22 of the 38 chances.
A strong start to the second set gave him a good footing and, although he missed his first match point, victory was confirmed when he converted the second.
Golubev had to come from a set down to book his place in the next round as he edged a decisive tie-break to beat Inigo Cervantes 3-6 6-3 7-6 (7-4).
Fifth seed Federico Delbonis only needed 53 minutes to ease past Dustin Brown as he recorded a 6-3 6-3 victory.
A beaten semi-finalist last year, Victor Hanescu will not get a chance to go one better this year as he made a first-round exit against Juan Monaco.
The Romanian's second serve was a weakness exploited by Monaco, he won 73 per cent of the points, and his 6-4 7-5 victory came after 84 minutes on court.
Meanwhile, Daniel Gimeno-Traver and Yann Marti will have to return on Tuesday after their match was suspended due to bad light.
Rain had hampered their attempts to finish the match and with the score 5-5 in the final set it was confirmed they would have come back and finish their contest in better conditions.