Barcelona coach Frank Rijkaard said his side's profligacy in front of goal was a concern after they only beat lowly Levante 1-0 at home on Sunday to maintain their narrow lead in the Primera Liga.
The defending champions dominated but failed to add to Samuel Eto'o's scrappy first-half effort, and almost conceded a late equaliser as goalkeeper Victor Valdes fumbled a cross.
The league's leaders and top scorers have only managed two goals in their last four games.
"To be only 1-0 up created a situation where we were forced to suffer and feel a little anxious," media reports quoted Rijkaard as saying on Monday.
"I am pleased because we created chances, but lately we have failed to score many goals. The games have been harder because we haven't scored as freely as we did before."
With six games left, Barca stayed top on 62 points, one ahead of Sevilla and two clear of arch-rivals Real Madrid, who between them bagged seven goals on Sunday.
Sevilla's bid for honours on three fronts continued apace as they overran Espanyol 3-1 at home.
They hit the bar and had a goal ruled out for offside in a scintillating first half, before securing the win after the break with goals from Antonio Puerta, Ernesto Chevanton and Jose Luis Marti.
With UEFA Cup and King's Cup semi-finals to contend with, as well as a trip to the Bernabeu next weekend, Sevilla coach Juande Ramos was cautious about his side's title challenge.
"When there are four or five games left in the league we will know how realistic our chances are. For the time being the UEFA Cup on Thursday is our priority," said Ramos.
Real's victory in Bilbao was their fifth in sixth games. In-form Dutch striker Ruud van Nistelrooy scored twice to take his tally for the season to 18 and coach Fabio Capello said his side were improving game by game.
"The manner and margin of the victory sent out a strong message as Barca and Sevilla had already won their games," said Capello.
"Most important of all we showed personality in a difficult game."
On Monday, Spanish daily El Pais summed up the title race saying: "While Barca suffered an anxiety attack against Levante, Real Madrid passed through San Mames like a whirlwind.
"Barca seem to be at their limit while their pursuers are at full speed."