Mitchell threw two touchdown passes to lead the Calgary Stampeders over the Toronto Argonauts 25-20 at McMahon Stadium.
Meanwhile, Smith was pressed into duty on the offensive line after both Edwin Harrison and Dan Federkeil went down in the second quarter with lower leg injuries.
"He already got the game ball," said Mitchell of Smith switching positions in the second quarter. "That was huge. That was amazing by him to step in and do that. Not many people can go out there and do that."
Smith played both offence and defence for the Concordia University Stingers before joining the Stampeders last year as a defensive lineman.
"In college I played both ways, so I was kind of used to the switching," said Smith, who also had to switch jerseys from No. 90 to 68. "When Dan went down, it was 'Hey get a jersey on, let's go, it's time to play offence.'"
Getting the win was great, but receiving the game ball was extra special for Smith.
"I'm going to hold it close to my heart," he said. "I might even sleep with it the first couple nights."
Jon Cornish ran for another touchdown for Calgary (2-1), which rebounded from a 29-11 road loss to the Montreal Alouettes on July 3.
Rene Paredes kicked a field goal for the Stamps, while Rob Maver added a single.
Toronto quarterback Trevor Harris threw touchdown passes to rookie receivers Kevin Elliott and Tori Gurley while Ronnie Pfeffer kicked a pair of field goals for the Argonauts (2-1).
"I just didn't play well tonight," said Harris, who completed 20-of-34 passes for 223 yards and one interception. "The Toronto Argonauts deserve better play from the quarterback and I need to be better. They're a good defence and it's just lack of execution on my part.
Neither team could get much going early on until Harris completed an eight-yard touchdown pass to Elliott late in the first quarter to cap off a seven-play, 78-yard drive.
Mitchell tossed a 43-yard pass to Eric Rogers to start off a nine-play, 102-yard scoring drive in the second quarter. Rogers completed the drive by catching a three-yard TD pass from Mitchell, before Paredes missed the convert.
The Stamps then regained possession when Jeff Hecht stripped the ball from Chad Owens at midfield. Josh Bell recovered the fumble and ran eight yards lateralling the ball to Fred Bennett, who raced downfield to the Toronto four-yard line.
After Cornish ran the ball into the end zone on the next play, Mitchell found Marquay McDaniel for a two-point convert to put the Stamps up 14-7.
Following a quick two-and-out by the Argos, Calgary struck again at 12:21 of the second quarter when Jeff Fuller reached over Toronto defender Akwasi Owusu-Ansah for a six-yard touchdown pass from Mitchell.
"It was big for us to get those touchdowns in that second quarter," said Rogers, who caught six passes for 114 yards. "Then we had those injuries and we kind of had to switch up what we do. We responded and the defence held them to two field goals in the second half and we got the win."
The Argos answered right back just over a minute later when Gurley caught a 44-yard touchdown pass from Harris.
After a 55-yard punt single by Maver, the Stampeders took a 22-14 lead into the locker room at halftime.
Pfeffer kicked a 48-yard field goal in the third quarter and added a 45-yarder early in the fourth to pull the Argonauts within two points.
Calgary killed the clock in the fourth quarter with an extended 13-play, 62-yard drive that was capped off by a 30-yard field goal by Paredes to secure the victory.
"From an offensive perspective, it just wasn't a clean game," lamented Toronto coach Scott Milanovich. "We just couldn't string together enough offensively to get the job done."
Notes: Stamps receiver Simon Charbonneau-Campeau also left the game with a leg injury in the third quarter. … With 56 yards on the ground, Cornish moved past Lovell Coleman and into fourth place behind Joffrey Reynolds, Kelvin Anderson and Earl Lunsford on Calgary's all-time rushing yardage list.