Saul Niguez's goal proved enough to secure Atletico Madrid a precious away victory over Group D rivals PSV, much to Diego Simeone's delight.
Saul Niguez grabbed the only goal of the game in the 43rd minute as the LaLiga side made a successful start to their campaign in Group D.
However, Atletico were only ahead at half-time thanks to goalkeeper Jan Oblak keeping out Andres Guardado's penalty.
PSV also had an early goal disallowed as the visitors - who knocked their opponents out of last season's competition - rode their luck to pick up three crucial points on the road.
"It was a hard game, we knew they're a very good side and they played like they did at the Calderon," Simeone told UEFA.com.
"We got the goal but weren't able to finish off the game in the second period on the counter but the three points are very important."
After two draws at the start of their domestic season, Atletico have now recorded back-to-back wins following the international break.
Simeone acknowledged there is still room for improvement, particularly as their next game in Europe sees them host fellow heavyweights Bayern Munich in the Spanish capital.
"We now have Bayern at home, who have just won, but today I'll enjoy the side's effort," he added.
"In the second period in particular it was a big effort. At the end they pushed on. We've played three games away this season and we're happy.
"It was a shame we couldn't finish on the break and we have a lot to improve upon, but we go home happy, above all win the win."