The champions came from behind to see off basement side Almeria 3-1 in a nervy display at the Nou Camp where two goals from Lionel Messi helped them maintain their eight-point advantage over second-placed Real.
Earlier, Jose Mourinho's team eased to a 3-0 victory at Athletic Bilbao but with seven matches left to play starting with next Saturday's 'clasico', time is running out if they are to deny Barca a hat-trick of La Liga crowns.
"It is a unique opportunity to strike a decisive blow," Guardiola told a news conference.
"If we lose (at the Bernabeu) Madrid will only be five points behind us with six left to play. The league will be very much alive.
"We need to play this match the same way we did last year or even the year before. They are a team with a great counter-attack, a large squad, many different options and with the ability to play in many different ways," added Guardiola.
"We'll have to make a huge effort to convince the players they need to go and win. My experience of the Bernabeu is it puts you under a lot of pressure. As far as I know there has never been a 'decaffeinated' Madrid-Barca game."
Next Saturday's match could be the first of four meetings in 18 days with a King's Cup final on April 20 and a strong possibility of the two clubs clashing again in the Champions League semi-finals on April 27 and May 3.
Mourinho, in his first year at Real, is seeking to end an impressive run of five consecutive wins by Guardiola in Madrid v Barca clashes since he took over at the Catalan club in 2008.
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