Andrew Ference's slap shot from the blue line missed the net but caromed off the boards and out the other side where Boyd sent the puck in from a sharp angle.
"I was just going to the net and hoping for a rebound, and it hit the back boards and came right to me and I've got to bury those opportunities," said Boyd, who had two assists in five games with the Flames earlier in the season.
Boyd was one of two forwards called up from Omaha of the AHL on Friday to take the place of Iginla (knee) and Chuck Kobasew (concussion), both hurt Thursday in a win over Florida.
"With a guy like Iginla out and Chuckie, you can't fill that void completely. You've just got to go out there and make the most of your opportunities," Boyd said.
Alex Tanguay scored into an empty net with 27 seconds remaining, after posting two earlier assists.
The Flames have won four of five and moved into sole position of second spot in the Northwest Division, one point behind Vancouver.
Like the Flames, the Stars iced a depleted lineup without defenseman Sergei Zubov (back spasms), who missed his first game of the season, and forwards Brenden Morrow (ankle), Mike Modano (hip), and Eric Lindros (ribs).
Dallas outshot Calgary 33-21 but ran into a familiar nemesis in goalie Miikka Kiprusoff.
"We had a lot of shots, a lot of opportunities, but he made some big saves again. That's why he's a top goaltender in the league," Sydor said. "We played well for a majority of the game but we needed to play well for a couple more minutes to take it into overtime."
Without Kobasew and Iginla, Ritchie moved up to the second line alongside Matthew Lombardi and Tanguay and logged a season-high 17 minutes of ice time.
"It's a huge character win for us," Ritchie said. "Going into the third period tied at 2-2 against a good hockey team, we just kept plugging away and Boydy got a huge goal for us."
The new trio wasted little time establishing chemistry as Lombardi and Tanguay set up both of Ritchie's goals.
Ritchie gave Calgary a 2-1 lead 1:17 into the second period. His first career two-goal game gave him six goals on the season, surpassing his previous high of five.
"Believe it or not, I used to be a goal scorer," said Ritchie, who netted 50 goals twice in juniors but has only 20 in 224 NHL games.
Dallas tied it at 11:15 of the second period with their second power-play goal in two chances. Eriksson and Jeff Halpern combined to set up Lehtinen circling out from behind the net. He tucked a shot behind Kiprusoff, who was trapped out of position.
Dallas recorded the first nine shots before the Flames' other callup, Carsen Germyn, registered Calgary's initial shot.
Despite being outshot 11-6 in the opening period, Calgary was tied 1-1 thanks to Ritchie's goal at 16:53. Similar to his first goal, Tanguay spotted Ritchie open in front for a one-timer
"When Tangs is throwing you passes right on the goal line, it's hard to miss those," Ritchie said. "It was really enjoyable playing with Lombo and Tangs. They're great players and make it easy for me."
Dallas opened the scoring at 9:09 when Sydor scored his first goal in 34 games.
Kiprusoff made 31 saves compared to 17 for Dallas' Marty Turco.
- The last game Iginla missed was Jan. 19, 2004. He had played 158 straight games
- The 11 games Iginla missed with a hand injury in 1997-98 marks the longest absence of his career.
- Calgary is 4-0-2 in the last six games without Iginla. In the 31 games Iginla sat out, the Flames are 15-11-5.