It was an excellent session for Red Bull, who saw Daniel Ricciardo and Daniil Kvyat take fourth and fifth respectively, ahead of the Ferrari of Kimi Raikkonen and the Force India of Sergio Perez. The Toro Rossos of Carlos Sainz and Max Verstappen, split by Lotus’s Pastor Maldonado, completed the top ten.
Q1 saw Rosberg pip Hamilton by 0.06s with 1m 16.528s to 1m 16.588s on the soft tyres, as Verstappen, Kvyat, Sainz and the rest of the field bar Ferrari had to use supersofts to make it through to Q2. Vettel was ninth with 1m 17.502s, with Raikkonen three spots further back on 1m 17.660s.
Sainz, however, will have to start the race from the pit lane after missing a mandatory invitation to the FIA weighbridge.
Massa made it through for the understeer-troubled Williams team, but Valtteri Bottas did not. His final laps were spoiled by traffic, leaving him unable to improve on 17th.
Sauber's Felipe Nasr was very fast very early on with a set of supersofts, but gradually fell back to 16th place with 1m 18.101s, which left him ahead of Bottas on 1m 18.434s and team mate Marcus Ericsson on 1m 18.513s.
Behind them, Will Stevens and Roberto Merhi had a great intra-team battle for Marussia, with the Briton gaining the advantage, 1m 20.655s to 1m 20.904s respectively.
Things began to heat up in the battle for pole in Q2. Hamilton was called back into the pits for more front wing to be added - an oversight his engineer held his hands up to - and then Fernando Alonso glided to a halt after Ste Devote just as team mate Jenson Button had momentarily gone fourth for McLaren. The Spaniard’s problem was likely mechanical, and left him mired in 15th.
Rosberg was quickest with a stunning 1m 15.471s, while Hamilton improved to second on 1m 15.864s after a messy session by his crew, and Vettel secured third with 1m 16.181s.
The battle to join that trio in Q3 was incredibly tight, but just as the final runs approached Rosberg locked his right front and went spearing into the Ste Devote escape road, triggering the yellow flags. That scuppered the hopes of several drivers, perhaps most notably Button, who had to back off and abandon his final effort to book McLaren's first appearance of the season in Q3.
Perez was the beneficiary, edging through in 10th on 1m 16.999s, whereas Romain Grosjean, Button, Nico Hulkenberg and Felipe Massa all faced disappointment despite really close times. They respectively lapped in 1m 17.007s, 1m 17.093s, 1m 17.193s and 1m 17.278s to take positions 11 through to 14.
To add to the drama, some of the teams then reported rain in the air as they prepared for the vitally important Q3 session. By prior intra-team agreement Hamilton led Rosberg out of the pits, and soon battle commenced.
The opening runs yielded 1m 15.304s for Hamilton, 1m 15.440s for Rosberg, and 1m 15.849s for Vettel - but Hamilton wasn’t finished. His second run yielded more improvement, and ultimately secured him a first F1 pole on the Monte Carlo streets when Vettel eased off and Rosberg blew his final effort by locking up heavily once again at Ste Devote.
Ricciardo was fourth on 1m 16.041s, all but matched by Red Bull team mate Kvyat in fifth on 1m 16.182s.
Raikkonen had hit the wall at Portier on his first run, having already complained of oversteer there, and had to be content with sixth on 1m 16.427s. Perez was an excellent seventh on 1m 16.808s, which he set on his first run - he had no tyres left to make a second attempt, but lost just one place.
Sainz took eighth for Toro Rosso with 1m 16.931s, ahead of Maldonado on 1m 16.946s and Verstappen on 1m 16.957s.
Thus, with Grosjean’s five-place grid penalty for a gearbox replacement, and Sainz's pit-lane start, the provisional grid will line up: Hamilton, Rosberg; Vettel, Ricciardo; Kvyat, Raikkonen; Perez, Maldonado; Verstappen, Button; Hulkenberg, Massa; Alonso, Nasr; Grosjean, Bottas; Ericsson, Stevens; Merhi, Sainz.
Watch Hamilton's pole position lap