Reigning Spanish champions Barcelona are three points adrift of table-topping Madrid heading into the mid-season break.
Madrid have yet to lose a match in LaLiga this term, having won late against Deportivo La Coruna, following their last-gasp draw at Barca on December 3.
Sergio Ramos scored in the 90th minute or later in each of those games as Sergi Roberto said fortune has favoured Madrid.
"I think that they have had a bit of luck so far," Sergi Roberto told RAC1.
"They have been scoring goals in the last minute. A game doesn't end until the final whistle, of course, and you can score then, but there have been a lot of games when they've been drawing and end up scoring in the last minute through a free kick or a corner.
"But for us it's positive mentally to end the year three points behind Madrid in the league. It's good to go into the break with a win. We're back in good form."
Barca are in form thanks to back-to-back wins following a stuttering run of three consecutive draws.
Lionel Messi and captain Andres Iniesta have been instrumental in the improved run of results, namely the former.
After losing out to Ronaldo for the 2016 Ballon d'Or, five-time winner Messi scored and assisted twice in the 4-1 rout of rivals Espanyol last week.
And Sergi Roberto talked up his team-mate, saying: "He is the best player in history. You can't compare him [with Cristiano Ronaldo].
"Beyond the Ballon d'Or, everyone knows that Messi is the best. He's light years ahead."
Sergi Roberto added: "Watching Andres and Leo when they're together is fantastic. It's a tandem the fans love to see because they create magic with the ball at their feet. Everyone knows the greatness of these two players.
"Andres is from the academy and he's spent many years with the club. You notice when he's not there. He's one of the team's most important players."