The Steelers had four scoring chances on their first four drives. They scored only 10 points, with the touchdown coming on a trick play on the final play of the first half.
Offensive lineman Alejandro Villanueva caught a 2-yard pass from kicker Chris Boswell as time expired in the first half to tie the Broncos 10-10.
Villanueva became the first Steelers offensive lineman to catch a touchdown pass since Ray Pinney in 1983, according to Ed Bouchette of the Pittsburgh Post-Gazette.
Still, Pittsburgh should have the lead. The Steelers have run 41 plays for 251 yards.
Pittsburgh reached the Denver 30 on their first drive, going 52 yards before stalling.
But Justin Simmons does what Justin Simmons does: He blocked a Boswell 48-yard field goal attempt in the first quarter. Simmons leaped over long snapper Kameron Canaday to prevent the field goal.
Simmons did the same thing against Justin Tucker and the Ravens earlier this season.
The Steelers drove 74 yards on their second possession and ended up 1 yard short as Xavier Grimble fumbled out of the end zone on a hit by Will Parks. The touchback gave Denver possession.
Pittsburgh went 56 yards to the Denver 23 on its next drive before settling for a 41-yard Boswell field goal.
On their final drive of the first half, the Steelers rolled down the field before Vance McDonald dropped a touchdown pass to set up a fourth-and-goal from the 2. Instead, of settling for another field goal, though, the Steelers called for the trick play.
The Broncos scored their touchdown on a 10-yard pass from Case Keenum to Matt LaCosse.
Ben Roethlisberger is 25-of-31 for 221 yards, the most completions by a Pittsburgh quarterback in a regular-season game since at least 1960.