Finland will now play Russia in the semifinals Saturday. After five Americans and four Finns failed to score in the shootout, Lehtinen calmly skated in and fired a shot under the crossbar to beat U.S. goalie John Grahame.
"It's kind of a relieved feeling," Lehtinen said. "I was a little nervous. But our goalie, (Kari) Lehtonen, kind of gave it to me easier because he saved the shot from the U.S. shooter before me."
Tuomo Ruutu, Pekka Saravo, Jari Viuhkola and Tomi Kallio scored in regulation for the Finns while Andrew Hutchinson, Tobias Petersen, Tyler Arnason and Lee Stempniak replied for the U.S.
"They came out hard at the beginning and took it to us but we battled back," Arnason said. "It's disappointing to lose in a penalty shootout but in a tournament like this, where you play a lot of games, it's part of the game I guess."
Kallio scored a power-play goal at 15:32 of the second period to put the Finns ahead 4-3, but Hutchinson scored the equalizer on another power play 14:20 into the final period, one-timing a cross-ice pass from Phil Kessel to send the game into overtime.
"Our team played with a lot of heart," U.S. coach Mike Sullivan said. "They showed a lot of resilience. There was no quit in them. This might have been their best game of the tournament even if they lost."
Ruutu made it 1-0 at 17:03 into the match, getting the puck away from the boards before firing a slapshot that got under Grahame's right leg.
Petersen tied the score 48 seconds into the second period with a short-handed goal, one-timing a Chad Larose pass over Lehtonen's glove.
The two teams traded goals twice more, with Saravo and Viuhkola scoring for the Finns and Arnason and Lee Stempniak tallying for the U.S.
Finland earned the bronze at the last worlds in Latvia. The U.S. got bronze in 2004.
Canada will play Sweden in Saturday's other semifinal after beating Switzerland 5-1 earlier Thursday.