The phrase "at once recognized" is correct and usable in written English.
It can be used to indicate that something was immediately acknowledged or identified without delay.
Example: "The painting was at once recognized as a masterpiece by the art critics."
Alternatives: "immediately acknowledged" or "instantly identified".
"Agon" was at once recognized as a beacon of radical modernity.
Lassalle at once recognized in the congress an opportunity to organize a "Suffrage Army".
Prime Minister Lloyd George at once recognized his abilities and made him minister of air.
Contemporary audiences at once recognized the play as a masterpiece, but its form was subjected to an unprecedented critical attack.
The first ceratopsian ("horn-faced") dinosaur remains were found in the 1870s by the American paleontologist Edward D. Cope, who named the animal Agathaumus, but the material was so fragmentary that its unusual design was not at once recognized.
Along the way, Howard thought he saw "familiar landmarks in unfamiliar places," and he could not read the names of streets as they passed, or the words "Emergency Room" at the hospital — though he at once recognized the picture of an ambulance over the door.
At once, Glyn recognizes his wife, Kath, but it is only upon closer inspection that he discovers that she and the man have their hands "closely entwined, locked together" behind their backs.
By some unexpected combination of character and conviction, Francis arrived on the scene with a relevance that the world grasped at once, perhaps recognizing this post-religious need in itself.
Early in the grand pas de deux for the young lovers (also in Central Park), the heroine holds a first arabesque in her partner's arms — and at once you recognize what ballet people call line, suddenly beaming forward, backward and outward into space.
He at once refused to recognize the legality of the court because "a king cannot be tried by any superior jurisdiction on earth".
Every so often, though, we're stopped dead by a crisis that we recognize at once as the genuine article; we recognize it not by its size (false crises can be made to look as real as big ones) but because in the course of it, for a measurable, anguished period — sometimes only minutes, sometimes hours, rarely as much as a day — nothing happens.
