Denver have stunned six-time Super Bowl champions Pittsburgh 29-23 in the NFL playoffs, while the New York Giants have beaten Atlanta 24-2.
Tim Tebow threw an 80-yard touchdown pass to Demaryius Thomas 11 seconds into overtime on Sunday to give Denver a 29-23 NFL playoff upset of six-time Super Bowl champions Pittsburgh.
Thomas caught the ball running across the middle and ran the last 60 yards into the end zone to put the Broncos, who lost their final three regular-season games, into the second round of the playoffs.
"I don't think it's the first time our offence has clicked in but it certainly was well timed," Broncos coach John Fox said.
"I don't think we reinvented the wheel. We just executed better.
"A lot of that was because of our quarterback. He stepped up and played well and was a big part of our winning that game."
Southpaw quarterback Tebow recaptured the magic of his mid-season six-game win streak, throwing for 316 yards and two touchdowns and running for another.
But his last play was his greatest, ending the shortest overtime in NFL playoff history.
"They made the significant plays that allowed them to win," Steelers coach Mike Tomlin said.
"It was what we expected. He did a nice job. A lot of guys did."
Denver will visit New England next Saturday while Houston will travel to Baltimore on Sunday in AFC second-round games.
In Sunday's NFC playoff game, Eli Manning threw three touchdown passes, two of them to Hakeem Nicks, asthe New York Giants advanced with a 24-2 victory over visiting Atlanta.
Manning completed 23-of-32 passes for 277 yards while Nicks caught six passes for 115 yards as the Giants won the maiden playoff game in their new stadium for their first home playoff triumph since 2000.
"It's special. It's a big win," Manning said.
"The defence came out awesome and we were able to get some things going in the second half."
New York's defence, among the NFL's worst against the pass despite finishing third in quarterback sacks, shut down 4000-yard passer Matt Ryan and sent Atlanta home after one playoff game for the second season in a row.
"It's incredibly disappointing but you have to deal with it," Ryan said. "You have to move on."
The Giants booked a second-round visit next Sunday to defending Super Bowl champions Green Bay.
New Orleans, on a nine-game win streak, go to San Francisco on Saturday in the other NFC matchup.
