Real Madrid suffered a second successive defeat and first at the Bernabeu in almost a year as Celta Vigo won Wednesday's Copa del Rey quarter-final first leg 2-1.
Real saw a 40-game unbeaten streak end on Sunday night with a La Liga loss to Sevilla and were beaten again as Celta won a sixth straight game, inflicting their hosts' first home defeat in the Copa del Rey in five years.
Iago Aspas' 64th-minute strike was cancelled out by Marcelo, but Jonny Castro scored what proved to be the winner one minute later.
There were few chances of note in the first half which saw Cristiano Ronaldo optimistically appeal for a penalty, when Facundo Roncaglia made contact in the area.
Celta's opening goal came on the counter. Theo Bongonda crossed towards Daniel Wass. It did not quite reach the intended target, but fell for Aspas who blasted the ball into the net.
The lead lasted five minutes. Marcelo struck a volley which deflected off Roncaglia to beat goalkeeper Sergio.
But parity was short lived. Aspas turned provider, finding Castro, who slid the ball beyond Kiko Casilla in the Real goal.
Sergio Ramos was perhaps fortunate to avoid a second yellow card for an elbow on Aspas as Real's frustration showed.
Karim Benzema was sent on by Zinedine Zidane, taking the number of Real attackers on the pitch to four. The France striker had a chance but blazed it high over the crossbar, leaving Real everything to do in the second leg next week.