Griezmann wasted two late chances in a 1-0 defeat at Sporting CP, Simeone's side progressing to the semi-finals 2-1 on aggregate despite their loss.
The France forward, sporting a newly shaven head, had scored 17 goals in his last 16 matches in all competitions but rarely looked like hitting the target in Lisbon.
But Simeone, who saw Diego Costa limp off early in the second half due to a hamstring problem and Lucas Hernandez suffer a facial injury, did not feel Griezmann was particularly below-par.
"It is impossible for Griezmann to be more decisive than he already is for Atletico," Simeone told reporters.
"We're very happy because once again, the team reinvented itself.
"Lucas and Costa got injured and the team kept on playing with a massive amount of effort.
"I didn't expect anything else from the match. Nowadays, nothing is easy. Sporting CP are a great rival.
"We could've scored two goals, but in the end we suffered to qualify for another European semi-final.
"Sporting have a great coach [Jorge Jesus]. We said it in Madrid. With important absences, we had to rearrange and the team responded. That speaks very well of Sporting.
"It makes us happy to have eliminated a tough opponent. The more you advance the harder the rivals are."
Atleti – winners of the Europa League in 2010 and 2012 – rarely threatened Rui Patricio's goal, with Fredy Montero's header giving Jesus's men hope of a comeback.
But Simeone preferred to focus on the positives as Atletico close in on a third appearance in a European final in the last five seasons.
"We live with enthusiasm and enthusiasm," Simeone added.
"I live with pride, that we are among the best in Europe, last year in the Champions League, this one in the Europa League. This is our reality now.
"For Atletico fans, it's an honour to be in another European semi-final."