VANCOUVER -- Two unheralded Saskatchewan players spoiled the B.C. Lions' guaranteed win night Sunday.

Backup quarterback Tino Sunseri's first CFL career touchdown pass to reserve offensive lineman-turned-tight-end Dan Clark sparked the Saskatchewan Roughriders to a comeback 20-16 victory over the Lions.

"For me to get the first one, it was really special," said Sunseri. "And, you have to give a lot of credit to the offensive line and Dan Clark for getting open on the certain play and blocking and all that. It was pretty exciting."

As a result, the 33,196 fans who attended Sunday's game will receive a free ticket to a future game courtesy of B.C. president Dennis Skulsky, who promised a Lions victory to the biggest crowd of the season at B.C. Place Stadium, which included many Riders' supporters.

The Riders (6-2) posted their fifth straight win and are now tied for second place with Winnipeg in the ultra-competitive West Division. The Lions (5-4) fell to third place.

Related: Instructions for redeeming free tickets

The Riders triumphed after they were forced to play the second half with rarely used backup Sunseri, a 25-year-old Pittsburgh native who is in his second season with the Riders, at the helm. After playing the entire first half, starter Darian Durant was sidelined with a hand injury that, he said afterwards, will be further evaluated upon the team's return to Regina.

"I never want (Durant) to get hurt, but we can all go in under a certain circumstance," said Sunseri, a University of Pittsburgh product who had never been to Canada before signing with the Riders on short notice a few days before training camp in 2013. "Everyone was coming up to me on the sidelines and saying that they had my back and everything like that. So I knew, with the work that we put in during the week, that we were ready for it."

The game was decided on the final play of the third quarter. With the Riders scrimmaging from the B.C. one-yard line, Clark lined up as an eligible receiver at tight end and got his hands on a high Sunseri pass in the end zone and held on, while falling backward.

It was the second CFL touchdown for Clark, a 26-year-old Regina native who scored one on a similar play in his rookie 2013 season.

"The play was called and I knew I just had to make the play and catch the ball," said Clark, who is usually a backup offensive guard.

The TD and Chris Milo's convert gave the Roughriders their first lead of the game and put them ahead to stay before Josh Bartel's punt single in the fourth quarter rounded out the scoring.

"With this atmosphere and the way the crowd was for this team, (the win) is huge for this team," said Clark.

The Roughriders prevailed after both teams lost their starting quarterbacks to injuries.

Durant completed 9 of 15 passes for 104 yards, but watched the rest of the game in uniform from the sidelines while sporting a brace on his right throwing hand.

Sunseri entered the game having made only seven pass attempts this season. But he still helped the Riders rally from a 13-9 first-half deficit.

Sunseri completed 8 of 13 passes for 86 yards and the one touchdown.

B.C. starter Kevin Glenn left the game with an undisclosed injury in the fourth quarter and was replaced by Travis Lulay, the team's usual starter who has been on a gradual-playing-time program in recent weeks following off-season shoulder surgery.

"Obviously, you knew that this game was going to be won and lost on the field - and they earned the win tonight," said Lulay, when asked how the Lions felt about Skulsky's spoiled promise.

Glenn completed 15 of 21 passes for 146 yards while Lulay went 4 for 8 for 27 yards. Lulay's last-second hail-mary attempt fell well short.

After rushing for 186 yards in a win in Regina earlier this season, the Lions only managed 56 total rushing yards Sunday. Andrew Harris, who entered the weekend first in the league in yards from scrimmage had only 11 yards on eight carries upon return from a one-game injury absence due to a sore ankle.

"That was a big difference from the game that we played in Saskatchewan," said Lulay. "We moved the ball effectively there. But, tonight, we couldn't consistently run the football, especially in the first half."

The Lions built an early lead with large help from returner Tim Brown, whose spot in the B.C. lineup was uncertain earlier in the week because of the Canadian and import player ratio. He returned the opening kick-off 68 yards to the Saskatchewan 50-yard line to set up a Paul McCallum 38-yard field goal just two and a half minutes into the game.

But, despite holding an early 13-3 lead, B.C. never scored an offensive touchdown and had to settle for three McCallum field goals for their other points.

Milo's four field goals accounted for the rest of Saskatchewan's scoring. While the Riders generally downplayed the spoiling B.C.'s guaranteed win, Saskatchewan defensive lineman Ricky Foley, a former Lion, took satisfaction from it.

"We're still (defending Grey Cup champs) until somebody beats us," said Foley. "Don't mess with the champs."