Tanguay made his NHL debut on October 5, 1999, against the Nashville Predators and scored his first point that night, recording an assist on a Claude Lemieux goal as part of a 3–2 Colorado win. He scored at least one point in his first five NHL games, including his first NHL goal on October 8 against Peter Skudra of the Pittsburgh Penguins. He was named to play in the YoungStars Game as part of 2002 NHL All-Star weekend, but did not play due to injury. Though he struggled at times adjusting to play in the NHL, he finished the season second in the league amongst rookies with 51 points, 19 behind rookie-leader Scott Gomez.