After graduating from the NJPW dojo, Tanahashi made his debut in October 1999, in a match against Shinya Makabe. Alongside fellow rookies Katsuyori Shibata and Shinsuke Nakamura, Tanahashi became known as one of the "new Three Musketeers". He became viewed as a big prospect and was given big wins over "lucha libre" legend Negro Casas in July 2000 and American Scott Hall in September 2001. His star continued to rise and in the 2002 G1 Climax (one of NJPW's most important annual tournaments) Tanahashi pinned Kensuke Sasaki in under two minutes. After this, Tanahashi was paired with Kenzo Suzuki in a tag team named the Kings of the Hills. This pairing was popular, but came to an end after a real life incident in November 2002 in which Tanahashi was stabbed in the back by Hitomi Hara, a TV Asahi news reporter. Tanahashi and Hara had dated one another, but in a meeting at her Tokyo apartment he tried to break off the relationship as he had started dating another woman, which led to Hara stabbing him twice. Hara later confessed she tried to kill Tanahashi and planned to commit suicide afterwards. Hara was charged with attempted murder and sentenced to four years on probation. Tanahashi was hospitalized, but would recover and ironically this incident may have been the best thing to happen to his career as the stabbing was widely reported across Japan and a strong interest to see Tanahashi return was created. On February 16, 2003, Tanahashi returned as a singles wrestler to a sold out crowd in Tokyo in a match against Manabu Nakanishi.