The influential midfielder was not impressed with his side's profligacy in front of goal, and believes it should have emerged victorious.
Cesc Fabregas opened the scoring for the Catalans after the interval, but they missed a number of chances to extend their lead, and eventually saw Raphael Varane help the Los Blancos to a hard-fought 1-1 draw.
"We let them off. I think we were the better side, we dominated and we created more scoring chances. It’s a strange feeling," Xavi was quoted as saying on the official Barca website. "We have been creating plenty of chances in recent Clasicos, but we aren’t accurate enough in front of goal. Scoring goals is key.
"Everything is still wide open. It will be the same story in the return leg, but we’ll try to be more effective."
The second leg is scheduled to take place on Feb. 27.
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