Victory moves Real two points clear of rivals Barca and with a game in hand.
However, Madrid's win was mired in controversy as goalkeeper Keylor Navas was extremely lucky to avoid an early red card before making a brilliant stoppage time save to deny Antonio Sanabria.
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Navas clearly cleaned out Darko Brasanac on the edge of the Madrid area as he raced from his goal after just 20 minutes, but referee Antonio Mateu Lahoz inexplicably waived play on.
The hosts didn't benefit from Navas's presence just four minutes later, though, as he bundled Sarabia's shot into his own goal having appeared to have the effort under control.
Cristiano Ronaldo ensured Madrid went in level at the break as he rose unmarked to power home Marcelo's cross from close range for his 26th goal of the season.
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Betis had chances to reestablish their lead early in the second-half with Ruben Castro's wild effort that flew over the best of them.
However, the visitors' chances of escaping with a point were dealt a huge blow when Cristiano Piccini saw a second yellow card 12 minutes from time.
And just three minutes later, fresh from scoring two vital away goals at Napoli to ease Madrid into the Champions League quarter-finals on Tuesday, Ramos powered home another Toni Kroos header for the winner.
Betis could still have salvaged a point, but Navas made amends for his early mistakes with a brilliant stop from Sanabria's powerful header.
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