The phrase "achieved only once" is correct and usable in written English.
It can be used to describe an accomplishment or event that has occurred a single time without repetition.
Example: "The record for the fastest marathon was achieved only once in 2020, and it remains unmatched."
Alternatives: "attained just once" or "realized only a single time".
She has ended up dominating the series: she has won three of the nine rounds, a feat achieved only once before, and taken second in another.
It also seems poised to win the London mayoralty – a feat the party has achieved only once in the previous four elections.
The feat has been achieved only once on the men's tour, by American Bill Scanlon, who beat Marcos Hocevar, 6-2, 6-0, in 1983.
So, he goes to Flushing Meadows looking for a Canada-Cincinnati-US Open treble achieved only once before, by Andy Roddick in 2003.
The capsule ejection system was repeatedly tested, but in-air payload recovery was achieved only once during the early years of the program: the capsule released by Discoverer 14 was retrieved on Aug. 18, 1960.
He could not convert, and so, once again, failed to make it to the fourth round in a Grand Slam event, a feat he has achieved only once, at the 2011 United States Open.
As a result, each lecture is clear and concise like the one we aspire to give every day but actually achieve only once or twice a semester.
After 16 to 20 hours in withering troughs that remove much of their moisture, the fresh leaves go into rollers that curl them into precise formations once achieved only by hand.
(That phrase either means nothing at all, since in some sense we have been in "a time of war" since at least 9/11, or else means something so doomed and horrific — full-scale permanent warfare in the Middle East — that, as the historian Andrew Bacevich has explained, it could be achieved only by changing everything once admirable about American life).
Once initial buy-in achieved, only then brings up issues of mental health.
Once clarity of thought process is achieved, only then should one venture into this terrain.
