"It's not for me to talk about them, but they are the most dangerous opponent we have faced so far," Enrique said. "If they keep playing at this level it would be silly not to consider them for the title."
While Diego Costa continued to impress, his strike partner David Villa had a game he will likely want to forget.
Celta goalkeeper Yoel Rodriguez turned back a number of his shots before Villa wasted a pass from Diego Costa that had left him alone with only the goalkeeper to beat. The 31-year-old Villa aggravated a case of arthritis in his left ankle just before the miss and immediately asked to be substituted in the 58th.
Atletico also lost captain Gabi Fernandez to a left knee sprain late, leading to the debut of French midfielder Joshua Guilavogui.
Rodriguez was particularly outstanding in the 25th when he blocked two clear opportunities following teammate Hugo Mallo's foul of Filipe Luis in the area.
Diego Costa stepped up to take the resulting penalty, but Rodriguez smothered his shot and was quick enough to retreat to his far post to swat away Villa's attempt to poke in the rebound.
But Rodriguez could do nothing when Celta's Alex Lopez knocked the ball back into his own area where Filipe Luis squared for both Diego Godin and Diego Costa to push the ball in. The goal was awarded to Diego Costa.
Diego Costa's second goal came when he neatly chested down a long pass, used one arm to brush off last defender David Costas, and fired the ball under Rodriguez.
"Costa is our soul," said Simeone. "He played a great game. He is constantly growing and can get even better."
Both Atletico and Barcelona can match Madrid's record start of nine consecutive wins to start the season in 1968 in the next round after the international break.