Pons rider Baldassarri started the race third, passed pole-sitter Marcel Schrotter off the line, made a movement on Xavi Vierge on Lap 2 and then didn’t give the lead before the final.
Luthi alternatively lost places from seventh on the grid, but he was able to gradually make up places as the race progressed.
After death Remy Gardner and Schrotter in quick succession, he had four laps to also pass Baldassarri, but he was not able to make a move.
He was all over Baldassarri on the last lap and needed a fantastic exit out of their previous corner, but he fell just short, settling for moment by 0.026s on his own return into Moto2 after one season in MotoGP.
Third place has been decided with an even smaller margin, as Schrotter denied Gardner his eponymous Moto2 podium by only two thousandths of another.
Baldassarri’s team-mate Augusto Fernandez has been an impressive minute with Sam Lowes taking sixth.
Alex Marquez charged from seventh to fourth at the early stages but ran out of pace at the end because he dropped back into seventh, followed closely by Luca Marini.
Italtrans rider Enea Bastianini has been the top rookie in ninth with Vierge, struggling for pace even more than team-mate Marquez, settling for 10th despite leading on Lap 1 ).
Brad Binder was likewise unable to maintain his premature location of fourth and at the end finished 12th.
The South African still stopped as the most notable KTM since he also 15th-placed Jorge Martin were the only two bikes of their brand to finish inside the top 20.
Martin’s former Moto3 rival Marco Bezzecchi crashed on the opening lap and was 26th at the finish line.