Rosberg won the Monaco Grand Prix from pole position on Sunday to take the championship lead back from Hamilton, who won the previous four races but was left infuriated by Rosberg's sudden and late accident the day before in qualifying.
The win was a fifth straight 1-2 finish for Mercedes, which has swept all six races this season, but that's the only type of harmony in the team. Tension is building, with Hamilton appearing unhappy before, during and after the race.
"It's a fierce battle between me and Nico and will continue that way," he said. "I'm going to keep my head up and keep pushing."
Rosberg drew his teammate's ire in qualifying when his late error led to a yellow flag ended Hamilton's chances of beating his time with a final flying lap.
Rosberg denied that he caused the incident intentionally and he was cleared of any wrongdoing by race stewards.
He went on to clinch his second victory of the season and fifth of his career, repeating his maiden GP win from pole here in Monaco last year. He leads Hamilton by four points in the drivers' standings, 122-118. Ferrari's Fernando Alonso, who was fourth, is already 57 points behind Hamilton.
"It's a special win, definitely, because Lewis has had the momentum with results," Rosberg said.
He finished 9.2 seconds ahead of Hamilton, who was 0.4 faster than Daniel Ricciardo's Red Bull. Four-time defending champion Sebastian Vettel's frustrating season with Red Bull continued as he abandoned the race on lap eight with a power unit failure.
Hamilton and Rosberg raced each other in their junior karting days, but they did not appear to shake hands after the race, and Hamilton looked visibly tense in the post-match race conference as he sat next to Rosberg.
He revealed that he and Rosberg had not even been in the post-qualifying debriefing together on Saturday.
"Nico did his big debrief before I got there, which is not what we normally do," Hamilton said. "Fortunately the engineers wrote down what Nico said."
Even at the drivers' pre-race parade they were at opposite ends of the circuit, and now they have six months left together until the end of the season, starting with the Canadian GP in two weeks' time.
Hamilton said after the race that he "drove fairly all weekend," which sounded like a veiled swipe at Rosberg.
During the race, a tense Hamilton snapped back at his team when told that Ricciardo was closing on him.
"I don't care about Ricciardo, what's the gap to Nico?" Hamilton said.
Hamilton would certainly have attacked more on another track. But overtaking on Monaco's tight and narrow 78-lap circuit -- which has the slowest average speed -- is so tough that 10 of the past 11 winners came from pole. The exception was Hamilton in 2008, the year he won the title.
Hamilton had sparked the escalation in the rivalry with Rosberg when he questioned his teammate's hunger on Thursday as he compared their different childhoods. Rosberg is the son of former F1 driver Keke Rosberg.
"I come from a not-great place in Stevenage and lived on a couch in my dad's apartment, and Nico grew up in Monaco with jets and hotels and boats," Hamilton said on Thursday. "If I were to come here believing that Nico is hungrier than me then I might as well go home."
Later, Hamilton explained what he'd meant.
"I said what gives me the hunger is where I grew up, in comparison to where Nico grew up," he said. "I was striving to come to live (in Monaco). I used to travel around with Nico on his dad's plane, I used to go on his boat, (in) his house. That gave me the desire to want that."
The race itself was also eventful as eight drivers failed to finish.
The safety car came out again on lap 26 when German driver Adrian Sutil's Sauber went into the barriers on the run down to the chicane. Mercedes took the opportunity to pit both their cars, and Hamilton seemed unhappy with the timing.
"We should have pitted on that lap (before)," he said. "But I knew you wouldn't call me in, guys."