Shelley Fabares, with “Johnny Angel”.
Montell Jordan did it, with “This Is How We Do It”.
The Box Tops, with “The Letter”.
The Fleetwoods, with “Come Softly To Me”.
Cutting Crew, with “(I Just) Died In Your Arms”.
Judging by the number of examples given in this thread, I think the answer to the OP is “many.”
I believe you’re correct; but I believe there’s more to add. For example, “I Believe”, from Fantasia Barrino, seems worth a mention.
The Tymes, with “So Much In Love”.
Mims, with “This Is Why I’m Hot”.
Frankie Goes to Hollywood’s first three singles all made it to no 1 in the UK
Yeah, I guess there are all kinds of examples if we go that way; for instance, it looks like Leona Lewis hit #1 in the UK with her first single, which apparently didn’t even get released in the US; but then her second single hit #1 in the US as well as the UK (along with at least half-a-dozen other countries).
But just in case that won’t meet the OP’s requirements, figure I’ll instead bump the thread today with quick mention of how George McCrae debuted at #1 in the US and the UK (and at least half-a-dozen other countries) with “Rock Your Baby”.
I believe Andy Gibb’s first three singles all went to #1 in the US.
Plenty of Sam Cooke’s Top 40 hits made it to #1 on the R&B charts — starting with his first (“You Send Me”) and his second (“I’ll Come Running Back To You”), and following those up with “Twistin’ The Night Away” and “Another Saturday Night”.
But it’s that first single that reached #1 both ways.
My immediate thought was a-ha as well. Nicely done.
[stabs self in ear with icepick]
…a-licky-boom-boom.
As for debut singles where even the singer “hated her own chart-topper,” Mary MacGregor managed to hit #1 with “Torn Between Two Lovers”.
I’m not sure this is legit here. The Morning After was written by 20th Century Fox staff composers for “The Poseidon Adventure”. It was well-known and won the 1972 Oscar for Best Original Song at the 1973 Oscar ceremony.
McGovern did a nice cover of it but it doesn’t seem to me to qualify here. She didn’t hit big with a song, she covered a well-known piece.
Hmm. What about what Erik Darling did for the Rooftop Singers?
That single wound up hitting #1, just like the first single that McGovern released; should neither qualify? Or both? Or one but not the other?
And, just to stretch this even further: the original version of ‘Young Love’ was recorded by Ric Cartey with the Jiva-Tones, which didn’t hit #1 and so doesn’t count; and Sonny James did a cover version, which did hit #1 but wasn’t his first single and so doesn’t count; but then Tab Hunter’s version, which was his first single, stayed No. 1 for a full six weeks and became a gold record. Billboard ranked this version as the No. 4 song for 1957. The success of this record led Warner Bros., where Hunter was a contract player, to form Warner Bros. Records.
And, in that vein but one step removed: Nelson, with “Love and Affection”.