Atlético should've scored at least a goal in the first half but didn't take their chances. It was obvious that the players were feeling tiredness from the Supercopa de España-games and that's completely normal when you're missing players on the bench who can do something off it.
It's not really a surprise to be honest. Rayo is a tough place and Atleti's missing Arda as well as Raúl García (who scores goals). It's been the same way during a long period in pre-season. The team needs strengthening in terms of attacking players who'll provide ability 1-on-1 but also in terms of movement and most important of all: pace. Hopefully they'll sign one attacking player more (we need two in my opinion but there's no more space on the wage bill) and integrate him quickly into the side for the restart of the league after the international break.
It'll probably be a much tougher start to the league this season but that's also to be expected. The pace of Diego Costa, Villa and Filipe Luís isn't replaced just like that.
A truly pathetic performance. We looked like a Segunda team in that second half. This can be partially attributed to fatigue from the game on Friday but it's evident that this team needs a bit more firepower before the transfer season ends.