Diego Simeone said the new Champions League format meant his Atlético Madrid team "absolutely had to win" their opening game, after José María Giménez's 90th minute header gave them a dramatic 2-1 victory over RB Leipzig.
Benjamin Sesko put Leipzig ahead on the counterattack in the 4th minute at the Metropolitano on Thursday, before the game's MVP Antoine Griezmann levelled after half an hour, and later set up Giménez for his winner.
Atlético will travel to Benfica in their next Champions League game, before facing Lille, Paris Saint-Germain, Sparta Prague, Slovan Bratislava, Bayer Leverkusen and Salzburg in the rest of the new league phase.
"This format means we absolutely had to win," Simeone told Movistar. "A draw today wouldn't do much for us. The format means you have to try to win, and if you can't, you have to get something.
"Those [teams] who win enough games will be in the top eight, and won't have to play two extra matches."
The top eight sides in the league phase will qualify automatically for the Champions League round of 16, while the teams finishing between 9th and 24th will compete in two-legged playoffs to progress.
Simeone's Atlético invested heavily in this summer's transfer market, signing Julián Álvarez, Conor Gallagher, Robin Le Normand and Alexander Sorloth, as they look to compete in the Champions League, where they were eliminated in last season's quarterfinals.
"From 65 to around 80 minutes, it looked like the game might get away from us," Simeone said. "And then Giménez scored. The performance was good, and if we'd drawn I would have said the same. We had different players trying things, they interpreted the game well, and we got an important, necessary win."
"We tried until the last minute," Griezmann said. "We know we have the players to score goals. We're on the right track, we'll keep going but it's just the start.
"MVP? My son will be happy, he loves playing with these trophies, he uses them as goalposts!"
Atlético travel to Rayo Vallecano in LaLiga on Sunday, before visiting Celta Vigo next week, and then hosting Real Madrid in the derby on Sept. 29.