Captain Ramos was sent off in the second half of Madrid's dramatic 3-2 loss at home to bitter rivals and titleholders Barcelona in the Spanish capital on Sunday.
Ramos saw red for a two-footed challenge on Messi with 13 minutes remaining and the five-time Ballon d'Or winner came back to haunt Madrid after settling the Clasico in the second minute of stoppage time.
Barca's win erased Madrid's three-point lead atop the table and full-back Carvajal was less than impressed.
"The sending off defined the game," Carvajal said post-match.
"We had managed to draw level and in the last passage of play we failed and have lost the game. The game had been end to end and we didn't have any luck."
Madrid stormed out of the blocks at the Santiago Bernabeu, Casemiro the unlikely scorer of the game's opening goal in the 28th minute.
Messi hit back within five minutes however, as Barca eventually took a 2-1 lead via Ivan Rakitic with 17 minutes remaining.
Just as Barca looked set to stun the Madrid faithful, James Rodriguez came off the bench and equalised in the 85th minute, only for Messi to pop up and score his 500th goal for the Catalan giants.
Carvajal added: "You have to congratulate them for the victory, but there is still a lot of the league left, we have played a game less and we have to make the most of it.
"Messi had a good game.
"The team has fought and had chances, we have to be calm and keep battling because we can still depend on only ourselves."