Mendy should have made the breakthrough shortly after the hour, but an abysmal finish from the left-back summed up a frustrating outing for Madrid, which nevertheless moved level on points with Barca, though it trails on goal difference.
Nabil Fekir went closest for Betis when he volleyed just past the post in the 21st.
Betis' standout performer Robles, meanwhile, believes Saturday's draw - on the back of their victory over Celta Vigo - can provide the struggling Andalusian side with a much-needed morale boost after they lost four of their previous five LaLiga matches before Saturday.
Madrid had a penalty appeal for handball turned down in the closing stages while Vinicius Jr. and Dani Carvajal were both thwarted in stoppage time by Betis goalkeeper Joel Robles.
What does it mean?
That said, a few players on Real Madrid did have strong performances, and it's time to praise three men who deserved to get something more than a point out of this game.
Madrid hosts Galatasaray in the Champions League on Wednesday.
Injuries have contributed to Hazard having a stuttering start to his Madrid career, but the Belgium star looks a shadow of his former self at the moment.
Had it stood, the goal would have been just Hazard's second of the season. A former coach of Villareal, Getafe and Elche, Escriba took charge of Celta in March and helped them avoid relegation but his side have only managed to win two games this season, drawing three and losing seven.
Betis is in 14th place.