A poor getaway in Barcelona meant Rosberg was unable to challenge Hamilton for the lead, despite a 730-metre run from the start line to Turn 1, the longest of the season.
Speaking to his team's website, the German pinpointed that moment as a key part of Hamilton's eventual 0.6s victory, and admits his starts are a growing concern, particularly as he would change little else in terms of his approach to a Grand Prix weekend.
"The start, unfortunately, was poor," said Rosberg, who also suffered a bad getaway and lost several positions in China, and lost out to Hamilton despite starting from pole in Bahrain.
"It's a bit of a weakness that we have at the moment," he continued. "It's just a bit inconsistent and now I've had a couple of bad starts in a row: three actually. That's costly and we need to work on that.
"The race was really lost in qualifying and at the start. Those were the two opportunities I had. On the last lap I could have gone for a kamikaze move but it wouldn't have worked. One more lap and I could have given it a go.
"Other than that, there's not much to change - I felt comfortable and the race pace was good."
Hamilton, meanwhile, said he had held on to his win despite Rosberg being "definitely quicker" over the 66-lap race.
"It was tough to keep him behind," the 2008 world champion said. "I struggled a lot with the balance and really had to rely on my engineers a lot more to give me the gaps and to try to work out where I could fine time.
"Nico was generally quicker this weekend but fortunately I was able to keep him behind."
As a result of his win, Hamilton moved into the overall standings lead for the first time this year, on 100 points to Rosberg's 97. Ferrari's Fernando Alonso is third, on 49 points, with Red Bull's four-time world champion Sebastian Vettel a further four points adrift.