On a wet track, Crutchlow gambled with hard tyres front and rear and it proved a masterstroke as the 30-year-old began to scythe his way through the field.
Most of the riders opted for soft wets but as a dry line began to appear in the final third of the race, they suddenly found themselves struggling to maintain their pace.
Movistar Yamaha’s Valentino Rossi also made a shrewd choice as he fitted a hard Michelin rear and the Italian also came on strong in the last part of the race, forcing his way through to second position.
Rossi finished 7.2 seconds behind Crutchlow at the end as the nine-time world champion moved ahead of team-mate Jorge Lorenzo in the championship standings, who endured a nightmare race.
Lorenzo, who was back on the rostrum in the previous round in Austria, was one of the few riders who came into pit lane to change bikes. The reigning world champion had been one of the fastest riders on track when he pitted and it proved the wrong strategy, with Lorenzo returning to the pits for a second time for another change, leaving him languishing at the rear and outside the points.
Title leader Marc Marquez finished on the rostrum in third on the Repsol Honda with another resilient performance to keep any damage to his championship advantage to a minimum, with Rossi only closing the deficit by four points.
Behind the top three, French rider Loris Baz also stormed through at the end to nick fourth place on the Avintia Ducati ahead of team-mate Hector Barbera.
Northern Ireland’s Eugene Laverty rode an excellent race to finish sixth on the Aspar Ducati ahead of Danilo Petrucci (Octo Pramac Ducati), while Austrian GP winner Andrea Iannone somehow limped over the line in eighth.
Iannone had enjoyed a lengthy spell in the lead on the factory Ducati but with a few laps remaining, it was clear he was struggling badly and TV footage showed his front tyre was completely destroyed.
His team-mate, Andrea Dovizioso, was forced into the pits when he was running inside the top three after the centre of his front tyre became worn out. He returned to the track on intermediates but retired from the race soon afterwards.
Suzuki’s Maverick Vinales and Tito Rabat on the Marc VDS Honda completed the top ten, with Yonny Hernandez (Aspar Ducati) and Dani Pedrosa on the Repsol Honda crossing the line in 11th and 12th respectively.
Britain’s Scott Redding rode impressively in the first half of the race as he challenged for the podium places, but the Octo Pramac Ducati rider was another rider who saw his prospects evaporate when he dropped off the pace after his soft tyres began to give up the ghost.
Redding eventually scored a point in 15th place behind Pol Espargaro (Monster Yamaha Tech 3) and Aprilia’s Stefan Bradl.
A frustrated Lorenzo finished 17th and last behind Alvaro Bautista (Aprilia).
Bradley Smith’s decision to pit and change to his second Monster Tech 3 Yamaha on slick tyres backfired and he failed to finish the race, as did Suzuki’s Aleix Espargaro.
Czech Republic MotoGP:
1. Cal Crutchlow
2. Valentino Rossi
3. Marc Marquez
4. Loris Baz
5. Hector Barbera
6. Eugene Laverty
7. Danilo Petrucci
8. Andrea Iannone
9. Maverick Viñales
10. Tito Rabat
11. Yonny Hernandez
12. Dani Pedrosa
13. Pol Espargaro
14. Stefan Bradl
15. Scott Redding
16. Alvaro Bautista
17. Jorge Lorenzo
Read more at http://www.crash.net/motogp/race-report/232960/1/crutchlow-masters-wet-for-brno-victory.html#dqjwI5w6FuZuizZz.99