Koke had already hit the visitors’ post in the first half when the referee judged Marc Albrighton’s foul on Antoine Griezmann had been inside the penalty area.
Replays showed contact was made outside the box but Griezmann duly stepped up to send Kasper Schmeichel the wrong way.
Fernando Torres slipped as the goal beckoned in the second half but, that chance apart, Atletico struggled to carve out clear-cut openings against a stubborn Leicester defence.
Robert Huth – who will be banned for the second leg after being booked – saw a shot blocked and Shinji Okazaki narrowly failed to make contact with a low cross in the best of Leicester’s rare raids forward.
Despite giving up 68% of possession and failing to register a shot on target, Leicester will take heart from their previous encounter with La Liga opposition.
They were similarly dominated by Sevilla in the first leg of their last-16 tie, but turned round the visitors’ 2-1 lead on a tumultuous night at the King Power Stadium.
Having reached the final in two of the last three years, however, Atletico are a team of greater pedigree and expectations than their compatriots.
With the meanest defence in La Liga and Griezmann poised to counter, Atletico are also ideally suited to withstand whatever atmosphere the Foxes fans whip up next Tuesday.