The hosts looked destined to secure a 1-0 win thanks to Luis Suarez's effort just after the break and went on to spurn a number of opportunities, with Neymar particularly guilty with one miss 20 minutes from the end.
But Ramos headed in Luka Modric's free-kick in the 90th minute to secure a draw for the visitors, keeping their six-point advantage at the top of La Liga.
"I don't know if it's a completely fair result," Ramos admitted. "But it was a great pass from Modric.
"It was really important to keep playing for a point. We worked hard to get the result.
"It was a very competitive game – both teams wanted possession in the first half and we maybe had more chances [before half-time].
"We weren't as efficient as we could have been, but a point is better than nothing and allows us to keep the advantage in the league.
"It was an intense game that we played to our limit and it is a reward for the good work we've been doing since the start of the season.
"There's a long way to go, but it's better to rely on yourself rather than others."