Lehtonen entered the record books upon being selected by the Atlanta Thrashers with the No. 2 pick in the 2002 NHL Draft. It represented the highest NHL Draft position ever for a European goaltender or Finland-born player.

He also made a bit of history with Atlanta. Lehtonen was the No. 1 goalie on the only Thrashers team to make the Stanley Cup Playoffs, in 2006-07 (they became the Winnipeg Jets for 2011-12). He went 34-24-9 with a 2.79 goals-against average and a .912 save percentage for Atlanta that season.

That season Lehtonen also set a Thrashers record for shutout minutes at 167:56, before giving up a goal in a 4-1 win against the Boston Bruins on Oct. 11, 2006. While in Atlanta he also became known for a unique array of mask designs, including Batman and "Transformers" themes.

Lehtonen's mask designs became a lot more subdued after he was traded to the Dallas Stars for Ivan Vishnevskiy and a 2010 fourth-round draft pick on Feb. 9, 2010. His play on the ice continued to improve, though.

In 2013-14 he was eighth in voting for the Vezina Trophy, awarded to the NHL's top goaltender, after he had 33 wins (tied for the League lead), a 2.41 GAA and a .919 save percentage in 65 games and 3,804 minutes (both League highs). He also was second in the NHL with 1,735 saves.

In 2014-15 Lehtonen won 30 games for the fourth time in five seasons and became the first goaltender in Stars history to win nine consecutive road games.