Wales worldwide Bale threw his future at the club into doubt just moments after his stunning two-goal, match-winning display in last May's Champions League final in Kiev.
Real, playing their first competitive game since all-time top scorer Cristiano Ronaldo left and Julen Lopetegui succeeded Zinedine Zidane as coach, pulled level through Karim Benzema in the 27th minute.
It didn't take long after the match for Antoine Griezmann to start rubbing it in, as the World Cup-winning France global shared an image (originally published by Bleacher Report) on his Instagram story showing Real captain Sergio Ramos anointing him the new king of Madrid/Europe.
"We hope this season will be greater".
But the coach said he was certain the team were still full of hunger to win silverware.
Real's new manager Julen Lopetegui endured a nightmare start as the European champions fell behind inside a minute to a superb individual goal from Costa.
Nevertheless, while Real and Barcelona have won the last five Champions Leagues between them, neither looks quite as strong as they have been in the recent past.
Lopetegui said: "It'll be a tough game both physically and tactically".
"He is motivated and is an important player who forms part of the team, and being a team is what is important".
Real, who beat Atletico in the 2014 and 2016 Champions League finals and also dumped them out of the competition in 2015 and 2017, looked set to pour more pain on their neighbours when Juanfran handled and skipper Sergio Ramos tucked the penalty away.
The FC panel answer your tweets on Real Madrid's needs, Bayern Munich's UCL expectations and whether Higuain or Ronaldo will score more this season. "We did a lot of good things, we need to focus on that and work, work, work for what comes next". "We will take the best decisions".
Real face an Atletico side who finished above them in LaLiga last term and also won the Europa League.