Starting in place of the injured Ricky Ray, the second-year quarterback showed tremendous poise under pressure against the CFL's No. 1-ranked defence, throwing for 253 yards on 21-of-25 passing.
The 24-year-old University of Cincinnati product, who spread the ball around to eight different receivers, also rushed eight times for 28 yards.
Meanwhile, the Argonauts bend-but-not break defence stymied Lions quarterback Travis Lulay and a B.C. offence that was toothless in the red zone.
With the victory, Toronto (3-2) snapped a six-game losing streak against B.C. (3-2).
Jason Barnes, Alexander Robinson and John Chiles caught TD passes for Toronto in front of a crowd of 20,064 at Rogers Centre, while rookie running back Curtis Steele, in the lineup for the injured Chad Kackert, rushed 12 times for 74 yards and two late TDs.
Lulay was 20-of-30 passing for 226 yards with an interception, while Paul MacCallum kicked four field goals for B.C. to move into fourth all-time on the CFL scoring list.
Toronto led 14-6 at halftime and never looked back on a rare Tuesday night game that concluded an awkward Week 5 of the CFL schedule.
After the Argonauts held B.C. to a field goal on their first possession of the second half, Collaros built on his two-touchdown first-half performance with another in the third to make the score 21-6.
The 12-play, 58-yard drive included a roughing the passer that helped set up Collaros' 23-yard touchdown pass to Chiles.
The Lions offence responded with a 10-play, 86-yard drive that was helped by a 40-yard pass completion from Lulay to Nick Moore, but Toronto's defence again held firm and forced a 10-yard MacCallum field goal that cut the Argonauts' lead to 21-12.
A 24-yard-field goal from Noel Prefontaine at 4:31 of the fourth then stretched Toronto's edge to 12.
The Lions were in scoring range again midway through the quarter, but the Toronto defence stepped up with another big play as Shane Horton recovered an Andrew Harris fumble inside the Argonauts' 25-yard line.
Lulay then fumbled deep in Lions territory and Steele went up and over for his first CFL touchdown with 2:24 left to play.
Steele added another TD run with under a minute to play from 11 yards out after the Lions failed to convert on a third down.
Toronto was without Ray and Kackert, who are both nursing knee injuries. The Argonauts have a bye next week and hope to have Ray back for their next game, a home date with the Montreal Alouettes on Aug. 8 at Rogers Centre. Kackert is expected to be out 4-6 weeks.
Trailing 3-0 late in the first quarter, Toronto linebacker Marcus Ball intercepted a Lulay pass to set up the Argonauts' first TD, a 22-yard strike from Collaros to Barnes that came just over two minutes into the second. On the scoring play, Collaros dropped back to pass and avoided the rush of the oncoming Adam Bighill to find Barnes between two defenders.
The Lions had a good looking drive going on their next possession but had to settle for a MacCallum's second field goal of the night, a 17-yard effort.
The Argonauts got the ball to midfield on the ensuing kickoff after executing a sneaky reverse and Collaros capitalized again by engineering a scoring drive that culminated in one-yard touchdown pass to Robinson at 10:48.
The Toronto defence then stopped a frustrated an disjointed Lions offence on successive drives to take a 14-6 lead into the break.
Notes: Collaros fumbled on his first possession to set up the Lions' opening field goal from MacCallum. ... Robinson and Chiles also scored their first CFL touchdowns for Toronto. ... The Lions' next game is Monday at home against Winnipeg. ... Lions guard Kirby Fabien was carted off the field with a leg injury in the first quarter. ... Toronto's victory over the Lions came July 23, 2010, a 24-20 victory at Rogers Centre. ... MacCallum moved passed Troy Westwood on the CFL's all-time scoring list with his first of two field goals in the third quarter. ... Collaros is the first Argonauts quarterback to win his first CFL start since Marcus Brady, who lead Toronto to a 24-14 victory over Winnipeg on July 15, 2003.