"I have no words, I was looking forward to this first goal", said the 20-year-old Melendo, who had come on as a substitute in the second half.
Barcelona routed Celta Vigo in the second leg of their round-of-16 clash behind a virtuoso performance from Lionel Messi, and the Blaugrana look to continue their winning ways against their neighboring foe.
"He suffered a significant incident at the start of the season in Getafe and now he has a small problem, that has little to do with the previous one, " Valverde said at a press conference, as quoted in the Spanish media.
He was also a Champions League victor with the English side in 2007/08, meaning his career tally in Europe's elite club competition stands at four wins overall. "We will try to turn things around". The penalty save reactivated the crowd - there was some tension and then they scored. Playing in a 3-4-2-1 formation, Espanyol had the first line of defence with five men and the second with four players holding their ground in midfield.
In better news, Valverde did reveal that Umtiti is making good progress and could be back "soon", although he will not be available for the short trip across Barcelona to Espanyol.
Barca fans were banned from the stadium but trouble briefly flared as Jasper Cillessen went down after being hit by a bottle top.
The Barca keeper tipped over a Marc Navarro free kick in the 83rd minute, before Melendo scored his goal which leaves Barca with work to do in next week's return leg.
Diego Costa gave Atletico the lead in the 73rd but the visitors equalized with an own-goal by Atletico goalkeeper Miguel Angel Moya in the 80th and secured the victory with a strike by Joaquin Correa after a breakaway in the 88th.