After Denver won the coin toss and elected to go on offense, the Broncos lined up and Tebow, the 25th pick in the 2010 draft out of Florida, found Thomas, 2010's 22nd pick out of Georgia Tech, behind two Steelers defenders over the middle.
Thomas stiff-armed cornerback Ike Taylor and sprinted down the right sidelines for a touchdown, which under recent NFL playoff rule changes handed the underdog Broncos an immediate win and a berth in the AFC divisional round next week against the New England Patriots.
Tebow went 10-of-21 passing for 316 yards and two scores with no interceptions. He also ran the ball 10 times for 50 yards.
Thomas made four grabs for 204 yards -- just the seventh 200-plus-yard receiving game in NFL playoff history.
The Steelers forced overtime with 3:48 remaining when Ben Roethlisberger hooked up with Jerricho Cotchery on a 31-yard scoring strike.
Roethlisberger completed 22-of-40 passes for 289 yards, a touchdown and an interception, but was sacked five times.
Isaac Redman gained 121 yards on 17 carries and Shaun Suisham went 3-for-3 on field goal tries for the Steelers.