BARCELONA, Jan 18 (Reuters) - Real Madrid's King's Cup hopes were hanging by a thread after they lost 2-1 at home to Celta Vigo on Wednesday and suffered back-to-back defeats for the first time under coach Zinedine Zidane.
Spain striker Iago Aspas, the top-scoring Spaniard in La Liga, gave the visitors a shock lead in the 64th minute by pouncing on a misjudged clearance by Marcelo and showing composure to fire past a sea of defenders.
Brazilian Marcelo made amends with a volley into the Celta net five minutes later but La Liga leaders Real were caught out again almost instantly on the counter-attack.
The lively Aspas robbed Lucas Vazquez around the halfway line and rolled the ball into the path of full back Jonny Castro, who confidently drilled a shot past Kiko Casilla to notch a second away goal for the Galicians.
Substitute Karim Benzema blazed over the bar from inside the area in the closing stages, failing to avoid a second straight defeat for Real who surrendered a Spanish record 40-game unbeaten run in all competitions on Sunday with a 2-1 loss at Sevilla.
Celta host Real next Wednesday in the second leg of the quarter-final tie with Zidane's side needing to win by at least two goals or with a 3-2 scoreline to advance to the semi-finals.
Earlier on Wednesday, Alaves took a huge step towards the last four by winning 2-0 at second division Alcorcon thanks to two goals in stoppage-time by forward Ibai Gomez. (Editing by Ed Osmond)