It will be crucial game to their ambitions to avoid relegation.
Depor lost 0-1 to Valladolid last weekend despite having more possession and more attempts on goal than their opponents.
"We dominated [in Valladolid], we dominated too easily, but dominating the ball means nothing," Vazquez told reporters.
"What is the point in keeping the ball if you do not spread the play, get into your opponents' area, penetrate and create chances? We have to improve in certain areas."
Vazquez stressed there is now no margin of error for his side, who are two points away from safety with three games left in the season, and underlined the importance of beating Espnayol in order to keep the pressure on Zaragoza, who occupy the final place above the relegation zone.
"This is a game we have to win, it's the only result we can afford. We have to focus on our own results. What would be the point of looking at the other teams' results if we don't win? We cannot afford to slip up."
Depor have been boosted by the news that midfielder Abel Aguilar has been passed fit after recovering from a calf injury.
Espanyol boss Javier Aguirre will demand that his players show the same aggression in Riazor as they did in their 1-1 draw with Real Madrid last weekend.
"We need to fight, fight and fight," he declared.
"After the game I told my players that they had reached the highest level, and they couldn't slip down again. It's my obligation to make sure their heads don't drop."
The Catalan club will have to play the match with a depleted side, after Hector Moreno was ruled out due to injury, joining a list of absentees that contains Joan Capdevila, Juan Forlin and Victor Sanchez, who are all suspended.
The coach said the team must beat Deportivo and try and finish within the top eight in the Primera Division, among the European places, while it is still mathematically possible.
"We can still get into Europe and for that reason alone we should go all out to try and get there.
"While there is still a glimmer of hope to get a place in continental competition, we will fight. We have to defend this institution."
However, even if Espanyol do finish among the European places, they are unlikely to compete in the Europa League, after the Spanish Football Federation denied them the UEFA licence, which they need in order to play European football, due to financial irregularities.
Aguirre was asked by reporters if he thought it was a shame they would not be able to play in Europe, and he responded emphatically: "A shame? That word is a euphemism. It would be a monumental disaster."