Massa will start last in Monaco.

MONACO, May 25 (Reuters) - German driver Nico Rosberg secured his third consecutive pole position in Formula 1 on Saturday, forming a one-two finish with his Mercedes teammate Lewis Hamilton on the front row for the Monaco Grand Prix.

It was Mercedes' fourth consecutive pole position, although their race results have been declining this season.

Three-time champion Sebastian Vettel of Red Bull finished third during the rainy session, and his teammate Mark Webber, winner of last year's race, will start alongside him.

Kimi Raikkonen, who is four points behind Vettel after five races and fighting for the title, starts fifth, and Fernando Alonso's Ferrari occupies sixth position.

Brazilian Felipe Massa will start in 22nd and last position.

See the starting grid for Sunday:

1. Nico Rosberg (Germany) Mercedes

2. Lewis Hamilton (Great Britain) Mercedes

3. Sebastian Vettel (Germany) Red Bull - Renault

4. Mark Webber (Australia) RedBull - Renault

5. Kimi Raikkonen (Finland) Lotus - Renault

6. Fernando Alonso (Spain) Ferrari

7. Sergio Perez (Mexico) McLaren

8. Adrian Sutil (Germany) Force India - Mercedes

9. Jenson Button (Great Britain) McLaren 1

10. Jean-Eric Vergne (France) Toro Rosso - Ferrari

11. Nico Huelkenberg (Germany) Sauber - Ferrari

12. Daniel Ricciardo (Australia) Toro Rosso - Ferrari

13. Romain Grosjean (France) Lotus - Renault

14. Valtteri Bottas (Finland) Williams - Renault

15. Giedo van der Garde (Netherlands) Caterham - Renault

16. Pastor Maldonado (Venezuela) Williams - Renault

17. Paul Di Resta (Great Britain) Force India - Mercedes

18. Charles Pic (France) Caterham - Renault

19. Esteban Gutierrez (Mexico) Sauber - Ferrari

20. Max Chilton (Great Britain) Marussia - Cosworth

21. Jules Bianchi (France) Marussia - Cosworth

22. Felipe Massa (Brazil) Ferrari

(By Alan Baldwin)