In Austin the Mercedes driver had to check his pace to save fuel, and in Mexico he had to do the same to control spiralling brake temperatures, having spent many laps trying to find a way past Carlos Sainz.
On both occasions when he was able to push harder once again his tyres wouldn't respond.
In Mexico, he finished sixth, having lost out to Lando Norris in the closing laps, while just managing to keep Daniel Ricciardo at bay.
"It was just a race dictated by tyres once again," he said when asked by Motorsport.com about his afternoon. "The car felt really strong, I was right behind Carlos, just couldn't quite make the overtake.
"But we had to back off because my brakes were overheating, as they were for many drivers. As soon as I backed off, I totally lost all the temperature in my tyres, and could never recover it.
"It was like driving on ice for the last 15 laps, and a pretty miserable feeling and very lucky to finish P6."
Russell said the positive was he understood why he had lost performance.
"It's never fun when you're the defending driver on the back foot," he noted. "Again just really struggled throughout that race with the tyres, and it was pretty clear as soon as I backed off, I lost all the grip, and I couldn't recover it.
"I'm not too concerned, because I know the reason for it. But it's been two race weekends in a row for two different reasons, last week was the fuel, and I lost my tyres because I backed off to manage the fuel, this weekend it was the brakes. That's at least some clarity."
Russell also said that the updated package Mercedes introduced at the US GP worked well in Mexico.
"We were strong here last year, we qualified on the front row," he said. "Probably should have had two cars on the podium last year. So it's definitely performing well.
"But this weekend has been a weekend about tyres, as it has been for everyone. Yesterday was a total surprise for many teams for good or for bad. I'm hoping Brazil won't be that sensitive."
