It was Russian rider Trofimov's first stage win since stage two of the Vuelta al Pais Vasco in 2009.
The 30-year-old Katusha rider pulled away from Gustav Larsson and Pim Ligthart at the front of a 13-man breakaway group on the Col de Manse climb, powering to the line on his own from 2km out and winning by 23 seconds.
None of the riders in the leading group were within striking distance of the general classification leaders, and Froome retains his lead at the head of an unchanged top six in the race.
“I can't believe I won. I knew this climb since the Tour de France last year. I planned to target it and ensured I was in the breakaway," said Trofimov afterwards.
"In the beginning of the stage, I saved my legs for the end, then I rode flat out on the climb. I gave the maximum. I'd like to win a stage at the Tour de France as well.”
Stage four results:
1. Yury Trofimov (Rus) Team Katusha 3:59:22
2. Gustav Erik Larsson (Swe) IAM Cycling 0:00:23
3. Pim Ligthart (Ned) Lotto-Belisol 0:00:25
4. Lars Petter Nordhaug (Nor) Belkin Pro Cycling Team 0:00:28
5. Peter Velits (Svk) BMC Racing Team "
6. Maxime Bouet (Fra) AG2R La Mondiale "
7. Jan Bakelants (Bel) Omega Pharma Quick Step Cycling Team "
8. Damiano Caruso (Ita) Cannondale "
9. Andriy Grivko (Ukr) Astana Pro Team 0:01:31
10. Ryder Hesjedal (Can) Garmin-Sharp "
11. Christian Meier (Can) Orica GreenEdge "
12. Romain Sicard (Fra) Team Europcar "
13. Imanol Erviti (Spa) Movistar "
14. Romain Bardet (Fra) AG2R La Mondiale "
15. Tejay Van Garderen (USA) BMC Racing Team "
- Sports & Recreation
- Pim Ligthart
- Yury Trofimov