Atleti beat the holders 1-0 at the Wanda Metropolitano Stadium thanks to a goal from Saul Niguez after four minutes. Liverpool struggled to respond because a usually prolific forward line was blunted, with Sadio Mane particularly out of sorts.
Mane was booked five minutes before the break for a foul on Sime Vrsaljko, and Klopp thinks it's obvious the hosts wanted to get the forward shown a second yellow card and ultimately sent off:
Klopp subbed Mane at halftime, replacing him with Divock Origi. The Liverpool boss spoke bluntly about why he replaced one of his star players so early:
Origi scored at the same venue when the Reds beat Tottenham Hotspur 2-0 in last season's final. Yet the Belgium international couldn't find the necessary space to punish an Atletico side defending with aggression and discipline.
Atleti boss Diego Simeone shaped his team into a compact 4-4-2 formation. The tactical setup succeeded in denying Liverpool space in wide areas, with strikers Alvaro Morata and Angel Correa keeping raiding full-backs Andy Robertson and Trent Alexander-Arnold penned deep.
Simeone's men also left few gaps between their two banks of four, with Saul working tirelessly in the middle. Meanwhile, tough-tackling Thomas Partey shielded the backline brilliantly:
Koke tucked in from the right to supplement the efforts of Partey and Saul, while former Real Madrid holding midfielder Marcos Llorente also excelled when he came on. The hosts also rarely wasted a chance to slow the game down, never rushing throw-ins or set pieces while protecting the early goal.
Klopp, who was booked by referee Szymon Marciniak for his protests, may not have liked the way Atleti went about it, but there was no denying how resolutely Simeone's group had absorbed pressure:
Liverpool bossed the ball, but didn't use it wisely enough with Mane and fellow forward Mohamed Salah subdued and off the pace. Mane made a goalscoring return from a hamstring injury during Saturday's 1-0 win away to Norwich City in the Premier League, but he was never allowed to settle in the Spanish capital.
Mane and Salah's problems were the main reason what had been a ruthlessly efficient Liverpool attack failed to click:
Atletico Madrid 1-0 Liverpool FT Liverpool failed to have a single shot on target for the first time in a game across all competitions since October 3rd, 2018 (vs Napoli) There wasn't a single shot on target between the two teams from the 27th minute onwards #UCL https://t.co/lx0idoAu2s
His team was ruffled by Atleti's knack for irritation, but Klopp remains bullish about Liverpool's chances of still going through when the two sides renew hostilities on Merseyside on March 11:
Klopp knows history is on his side after last season's dramatic comeback against Barcelona in the last four. Liverpool overcame a 3-0 deficit to beat the Blaugrana 4-0 at Anfield and reach the final.
Even so, Simeone and Atletico also have an enviable history for upsets in this competition. They beat Barca and Bayern Munich in consecutive knockout ties en route to the 2016 final.
Atleti also won 3-1 at Stamford Bridge to eliminate Chelsea in the 2014 semi-final. Diego Costa and Koke were in the lineup that night in west London and are still at Simeone's disposal.
So are Saul, Partey and Correa, who played when 10-man Atletico earned a 1-1 draw away to Arsenal in the UEFA Europa League semi-final in 2018. The Spanish club settled the tie at home and eventually won the trophy.
Simeone knows the formula for defying the odds in Europe. He was able to inflict just a third defeat in all competitions this season on Liverpool despite being without injured duo Joao Felix and Kieran Trippier.
If there is one team who won't be intimidated by the Anfield roar, it's Atletico.