The Swiss rider was victorious after taking the lead into Turn 1 from seventh on the grid of an interrupted race, after the red flags were shown at one-third distance in the original start.

With the first part of the race kicking off in dry conditions, poleman Mattia Pasini led the bulk of the early running before rain arrived on the seventh lap of the scheduled 20.

The Italian was then passed in quick succession by Franco Morbidelli and Miguel Oliveira at the start of the eighth lap, and had slipped to fourth behind Alex Marquez when the race was halted on lap 8.

However, with grid positions for the six-lap restart dictated by the standings at the end of the last completed lap, Pasini lined up on pole from Morbidelli and Oliveira.

Luthi had worked his way up from 11th on the original grid to take the restart in seventh, and surged to an immediate lead he would never lose.

Three laps into the restart, the Interwetten rider was three seconds clear of Marquez, and he took the finish line 4.991s clear of the Spaniard.

KTM's Oliveira completed the podium a further two seconds back, as points leader Morbidelli (Marc VDS) surprisingly faded from podium contention.

The Italian found himself bullied down to ninth place on the second lap of the restart, and could only recover one position to eighth after that, making Brno his worst finish of 2017 so far.

Morbidelli's troubles paved the way for Luca Marini (Forward) to come fourth ahead of Xavi Vierge (Tech 3) and Simone Corsi (Speed Up), while Francesco Bagnaia, who had also been in the running for a podium, slipped to seventh on his Sky Racing VR46 machine.

Completing the top 10 were Remy Gardner (Tech 3), son of 1987 500cc champion Wayne, and US rookie Joe Roberts, making his grand prix debut at AGR in place of Yonny Hernandez.

Pasini crashed out on the opening lap of the restart, while Sandro Cortese and Dominique Aegerter were non-starters after retiring during the initial start.

Race results:

Pos.	#	Rider	Bike	Time/Gap
1	12	Thomas Luthi	Kalex	13'39.036
2	73	Alex Marquez	Kalex	4.991
3	44	Miguel Oliveira	KTM	6.983
4	10	Luca Marini	Kalex	9.190
5	97	Xavi Vierge	Tech 3	11.064
6	24	Simone Corsi	Speed Up	15.779
7	42	Francesco Bagnaia	Kalex	18.431
8	21	Franco Morbidelli	Kalex	19.743
9	87	Remy Gardner	Tech 3	19.843
10	20	Joe Roberts	Kalex	20.168
11	9	Jorge Navarro	Kalex	20.372
12	41	Brad Binder	KTM	20.547
13	5	Andrea Locatelli	Kalex	21.657
14	89	Khairul Idham Pawi	Kalex	22.940
15	55	Hafizh Syahrin	Kalex	24.056
16	49	Axel Pons	Kalex	24.192
17	45	Tetsuta Nagashima	Kalex	24.441
18	7	Lorenzo Baldassarri	Kalex	25.607
19	27	Iker Lecuona	Kalex	26.483
20	40	Fabio Quartararo	Kalex	26.769
21	62	Stefano Manzi	Kalex	28.069
22	98	Karel Hanika	Kalex	28.167
23	19	Xavier Simeon	Kalex	28.304
24	30	Takaaki Nakagami	Kalex	29.463
25	32	Isaac Viñales	Kalex	29.795
26	6	Tarran Mackenzie	Suter	30.353
27	37	Augusto Fernandez	Speed Up	30.555
28	57	Edgar Pons	Kalex	30.815
29	2	Jesko Raffin	Kalex	38.907
Ret	54	Mattia Pasini	Kalex	-
NS	11	Sandro Cortese	Suter	-
NS	77	Dominique Aegerter	Suter	-