Formula One stewards summoned Mercedes to a hearing afterwards but, after reviewing video evidence, decided no offence had been committed.
The German had locked-up on the way into Mirabeau during the key final seconds of qualifying and skidded down the escape road, bringing out yellow warning flags that forced other drivers to slow.
The excursion, with Rosberg then putting the car into reverse, came just as Hamilton - behind him on the track - was on his final quick lap.
Hamilton, winner of the last four races but never before on pole in the principality, had been faster through the first sector but had to settle for second place on the grid for the season's showcase race.
"I'm happy it worked out. Pole at home is fantastic - it couldn't be better," a smiling Rosberg, last year's winner from pole and Hamilton's closest title rival, told reporters.
"I'm sorry for what happened to Lewis. I didn't know where exactly he was. But once I was reversing I didn't see who was coming up. Of course it's not great, but that's the way it is."
Hamilton, a forced smile on his face at the post-qualifying news conference, said it was 'ironic' for his rival to secure pole in such a fashion.
Speaking later to the BBC, the Briton went further. Asked whether he felt Rosberg had done it on purpose, he replied: 'potentially'.
However, Mercedes motorsport director Toto Wolff rejected that: "I don't think anybody does that deliberately in modern Formula One," he told reporters.
"He (Rosberg) missed his braking, which was in order to beat his team mate, and he took the exit. That's it. There is nothing to add.
"That moment is very intense when you lose out in qualifying to your team mate, but give it half an hour and he will have calmed down."
The incident nonetheless revived memories of Michael Schumacher's infamous 2006 pole lap when the seven-times world champion blocked the Rascasse corner and prevented Renault's Fernando Alonso from going faster.
On that occasion, Ferrari's German driver was sent to the back of the grid for an 'incorrect action'.
Rosberg, who has said he knew he had a 'banker' lap from earlier in the session and had just pushed a little too hard.
"I just locked up the outside front I think it was, or the inside, and that put me off line. I was still trying to make it but then in the last moment I had to turn out."
Hamilton, who said only days ago he was hungrier than his team mate for the title, has a three-point lead after five races, all won by Mercedes who have also started all from pole.
With Mercedes so dominant, the driver pairing is the talk of Formula One with all eyes watching for signs of their intense rivalry shifting up a gear into open feuding.
Comparisons have been made with the highly combustible 1988/89 McLaren pairing of Ayrton Senna and Alain Prost, who clashed infamously on the track while fighting for the title.
Hamilton, a boyhood fan of Senna, recalled that famous feud when asked whether he and Rosberg needed to sort things out.
"I don't know if Senna and Prost talked about it, but I quite liked the way Senna dealt with that so I'll take a page out of his book," he said, without elaboration.
Australian Daniel Ricciardo will start in third place, the clean side of the track, for Red Bull with quadruple world champion team mate Sebastian Vettel alongside.
"I think all three of us don't seem to be too pleased with ourselves," observed Ricciardo, sitting alongside Hamilton and Rosberg at a post-qualifying news conference.
The Ferrari pairing of Alonso and Kimi Raikkonen filled the third row.
The stewards were given more work on an eventful afternoon.
Felipe Massa was furious when Caterham's Swedish rookie Marcus Ericsson rammed his Williams at Mirabeau in an incident that meant he missed the second phase and qualified 16th.
"I gave him the space and he went over my car. I don't know what more there is to say. The race tomorrow will be very tough. I feel disappointed," said the Brazilian.
Ericsson was ordered to start from the pit lane and handed two penalty points.
Russian rookie Daniil Kvyat, who qualified an impressive ninth for Toro Rosso despite skidding into the barriers at the tunnel exit in the first phase of qualifying, was reprimanded for impeding the Lotus of Venezuelan Pastor Maldonado.
Danish rookie Kevin Magnussen qualified eighth on his Monaco F1 debut but 2009 world champion team mate Jenson Button, a former winner, was only 12th for McLaren.
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