Navas escaped a red card for fouling Darko Brasanac, then spilled Antonio Sanabria’s shot into his own net.
Cristiano Ronaldo headed Madrid level from a Marcelo cross before half-time.
Betis defender Matteo Piccinini was sent off for dragging back Lucas Vazquez with 12 minutes left, before Ramos powered in a Toni Kroos corner.
Morata cannot Bale out Madrid – but Ramos can
Captain Ramos has made a habit of scoring vital goals for Zinedine Zidane’s side this season – most notably a last-minute equaliser against Barcelona and a late winner against Deportivo, both in December.
The centre-back’s power from set-pieces proved vital as Real did not quite click in attack without the suspended Gareth Bale, and with Karim Benzema named among the substitutes.
Alvaro Morata, given a chance from the start, was unable to make an impact and was replaced by Benzema with 20 minutes left.
Ronaldo provided his usual threat, heading a fine equaliser and seeing another goal ruled out for offside.
But it was Ramos who led by example, as Zidane’s side took advantage of Barcelona’s surprise 2-1 defeat at Deportivo earlier on Sunday to regain top spot.
Real Betis were beaten 6-1 at home by Real Madrid in October, not long before head coach Gus Poyet was sacked.
This was a much-improved display under the guidance of Victor Sanchez, and they looked for a long time as if they would leave with at least a point.
They did not create many chances – although the lively Ruben Castro did fire a good one well over in the second half.
As the game wore on, their defence became increasingly stretched. Centre-back German Pezzella made a superb goal-saving challenge to deny Ronaldo on the edge of the area when any mistiming would have meant a red card.
In the end, the red card went to Piccinini. Already on a yellow, he was booked again for dragging back Vazquez, as the substitute tried to latch on a sublime Marcelo pass.
Navas nightmare ends in redemption
All goalkeepers dread the kind of mistakes that Madrid goalkeeper Navas made during five, crazy first-half minutes.
The Costa Rica international was incredibly fortunate not to be sent off following his first-half collision with Brasanac – having missed a through pass with an attempted header and then blocking off the Betis striker.
Navas’ night then got worse seemed to have gathered Sanabria’s shot, which was straight at him. But then, inexplicably, he allowed the ball to squirm from his grasp, and fumbled it over the line.
It was a goalkeeping howler right up there with the very worst – and unfortunately for Navas, it is one that will become a YouTube classic for all the wrong reasons.
Yet he made amends right at the end with a fine save, diving to his left to keep out Sanabria’s header and ensure a home victory.
- Shots on Target