Betis were knocked out of the cup at the quarter-final stage by Atletico Madrid in midweek and Jemez believes by keeping possession and playing at a high tempo Rayo can expose any tiredness that might be prevalent amongst the visitors.
He said: "Betis are a difficult opponent and against them we need to continue doing what we have done until now and that it what we want.
"They are a very attractive game that will require an extra effort from us, although my team is already too generous in its effort, I am meticulous and think they can still do more.
"To win we need to try and make their injuries and the possible tiredness from their participation in the Copa del Rey count in our favour, although I don't expect it to be easy.
"If we are capable of imposing a high tempo we will have a chance. We need to try and have the ball and make them run."
The hosts will still be without the injured Nacho and Leo Baptistao but both Alejandro Dominguez and Alejandro Galvez return from suspension after missing the 2-0 defeat to Granada last weekend.
Meanwhile, Betis boss Pepe Mel does not believe the Betis faithful should be downhearted at their cup exit as Los Verdiblancos still sit fourth in the table.
He told the club's website: "I see the Betis fans in the street and they are happy. I think we have done things well.
"It is not a drama to fall against Atletico and we had our chances. We have 35 points and we are fine. The Betis fans know what it is really like to be doing badly.
"We haven't had luck in the last few games against Rayo. Here they were the deserved winners.
"They are a team that do things well, they play good football and they are very quick on the transition so we have to be prepared and attentive."
Mel will be without nine first-team players for the trip to Vallecas as Paulao, Mario, Angel Lopez and Eder Vilarchao have become the latest players to be ruled out through injury, whilst Ruben Perez is suspended and Nosa Igiebor remains away with Nigeria at the African Nations Cup.