...Baby One More Time — Britney Spears (1998)

No other pop debut in the 1990s outperforms #9 in sheer cultural force: Britney Spears's '...Baby One More Time' sold 2.8 million copies in its first year in the U.S. alone, rewriting the rules for teen pop. Max Martin's production—a hypnotic mix of shuffling percussion and a descending synth hook—turned a school-corridor fantasy into a global anthem. The song's music video, featuring Britney's iconic schoolgirl outfit, became a defining visual of the decade, setting a benchmark for pop star image-making that remains unequaled. It topped the Billboard Hot 100 for two weeks and launched Spears as the best-selling teen artist of the era, eventually moving over 10 million units worldwide. For a debut single, its longevity is extraordinary; it still streams over 500,000 times daily on Spotify, faster than the average 1990s pop track.