Even though they could only draw with Bernd Schuster's side last time out, the midfielder is certain things will be different for Valencia at Mestalla - provided they do not drop their intensity against the Catalans.
"If we play with the same level of intensity and energy and create the same amount of chances we have been creating recently, we will have a much higher chance of winning than drawing or losing," Parejo told reporters.
"With the game at home and with our fans behind us, everything will be much easier."
The match is Juan Antonio Pizzi's fourth league game in charge since taking over at Valencia, and the initial euphoria from his first game in charge - a 2-0 win at home to Levante - has been tempered somewhat by a defeat at Celta and the draw at Malaga.
Parejo admitted it was vital to get back to winning ways against Espanyol, with the club nine points away from the European places.
"After a draw and a defeat, the game has become as important as a cup final and we need to get the three points," said Parejo.
Striker Helder Postiga and midfielder Sofiane Fefhouli are set to miss the game through injury, while Eduardo Vargas, the Chile international who has joined the club on loan from Napoli, will watch from the stands.
Juan Rafael Fuentes and Simao Sabrosa return for Espanyol after being rested for the midweek Copa del Rey defeat to Real Madrid, while Joan Capdevila and Manu Lanzarote have been left out of the squad, joining David Lopez (hamstring) on the sidelines.
Javier Aguirre's side are one point and one place above their opponents, who they beat 3-1 at Cornella El-Prat back in August, and the Mexican coach told reporters: "We want to defend our position in the table.
"We have to remember that Valencia have spent many years playing in Europe and they have a big budget. But we played well against them here and I hope that victory will encourage us."