Seconds later, teammate Erik Cole fired the puck past Vancouver Canucks goalie Ryan Miller.
That was a two-goal swing in a game the Stars won 6-3 on Tuesday night. Lehtonen prevented a short-handed score, and Cole put in a goal on the same power play. Instead of being tied 1-1 in the first period, Dallas led 2-0.
"That's the ultimate tradeoff," Stars coach Lindy Ruff said. "They're either coming back or we go the other way and get one. A lot of times you see that, when one big save leads to a goal going the other way.
Cole finished with two goals, and Lehtonen with 43 saves.
"(Lehtonen) made some great saves. He was our best player, by far," Ruff said.
Dallas scored five goals on only 12 shots against Vancouver starting goalie Ryan Miller to drive him from the game just 1:17 into the second period.
"I didn't like my overall positioning on Cole's goal," Miller said. "But after that, it was just a series of tough breaks."
He entered the game with a 3-0-0 record and 1.95 goals against average.
Cole gave the Stars leads of 2-0 in the first period and 6-1 in the second. It was his first two-goal game since last New Year's Eve.
Lehtonen's 43 saves were a season high, and six off his career high. Vancouver outshot the Stars 46-28.
"A 6-3 win and your goalie has to stop 40 shots," Cole said. "They kind of got a little bit of a push, and they were able to take some risks. "Ryan Garbutt, Tyler Seguin and Jamie Benn each had a goal and an assist for Dallas, and Shawn Horcoff assisted on both of Cole's goals."
Radim Vrbata, Zack Kassian and Jannik Hansen scored for the Canucks.
Garbutt scored the first goal at 4:08 of the first. He skated into the right faceoff circle and sent the puck off a defender and past Miller.
The Stars then avoided power-play disaster when Lehtonen stopped Hansen. Cole scored from the top of the slot at 17:46, with 9 seconds left on the power play.
The period ended 3-0 Dallas after Miller was entangled with a teammate and Tyler Seguin shot over the goalie at 19:17.
In a wide-open second period, the Stars outscored the Canucks 3-2. Vancouver trailed 6-2 despite outshooting Dallas 30-19 in the first two periods.
After Benn and Cody Eakin scored 29 seconds apart in the second, Vancouver coach Willie Desjardins replaced Miller with Eddie Lack. He made 15 saves over the final 38:43.
"They didn't get lucky goals," Desjardins said. "They went to the net and they got chances. I didn't think we gave up. That's the only positive."
Vrbata scored the Canucks' first goal at 3:39, and then Cole came back with his second goal at 4:44. Vancouver moved within 6-2 at 13:55 on Kassian's goal.
The Stars won all three games between the teams last season and have outscored the Canucks 23-7 since their last loss to Vancouver on April 18, 2013.
Dallas won at home for the first time this season to improve to 1-0-2.
NOTES: Benn has 12 points (five goals, seven assists) in his last eight games against Vancouver. . Stars D Jamie Oleksiak played in place of Patrik Nemeth, who will miss the rest of this season following surgery to close a laceration on his right arm. . Desjardins coached Nemeth and won the AHL's Calder Cup last season with Dallas' top affiliate, the Texas Stars. Assistant coach Doug Lidster was on Desjardins' staff at Texas, and assistant Glen Gulutzan is a former Dallas head coach. . The line of Vrbata, Daniel Sedin and Henrik Sedin has totalled 21 points (7 goals, 14 assists) in the season's first four games.