DENVER -- Shelby Harris pushed and shoved and stuck his hand high in the air, hoping for the best. And he managed to get a piece of the ball.

The big, burly defensive end blocked Younghoe Koo's second 44-yard field-goal attempt in the final moments after the rookie kicker's successful first kick was waved off because of a last-second timeout, preserving the Denver Broncos' 24-21 victory over the Los Angeles Chargers on Monday night.

"It feels great," Harris said. "I've actually blocked a couple of field goals in college. It's like, one, two, three, put your hand up. It's like a craft."

The game was the season opener for both teams.

Vance Joseph's icing of Koo made him a winner in his head coaching debut with the Broncos and allowed Denver to withstand a furious fourth-quarter rally led by the Chargers quarterback Philip Rivers.

"That was big," Broncos wide receiver Emmanuel Sanders said. "Him calling that timeout was huge. That's your first game as a head coach, to call that timeout, and the guy comes and blocks the kick to end the game, that was just cool. But I'd rather it just be a blowout. We're going to fix that."

The ending left the Chargers with a loss in their first game since moving in the offseason to Los Angeles from their longtime home in San Diego. Anthony Lynn, also making his head coaching debut for the Chargers, will try again for his first win next week.

"We just waited too long to get started, but then you could feel it," Rivers said. "We've been on both sides of those kind of games where teams start roaring back like that. We were going pretty good. We just came up short.

"It's too bad because Koo drilled the first one and they called timeout and I think he drilled the second one, too. At least that's what it looked like to me because it was going right down the middle. And I think if we get to OT, we would have finished it off, but we didn't get that chance."

Denver quarterback Trevor Siemian completed 17 of 28 passes for 219 yards, including scoring tosses of 5 and 6 yards to Bennie Fowler III.

Rivers completed 22 of 33 for 192 yards and three touchdowns with one interception.

Trailing by 17 points going into the fourth quarter, the Chargers scored 14 points in little more than a minute after forcing Denver turnovers. Los Angeles pulled within 24-21 with seven minutes left to play.

Safety Adrian Phillips' interception of a Siemian pass that was tipped in the air off cornerback Desmond King's cleat led to a 5-yard touchdown pass from Rivers to Keenan Allen with 8:10 left.

The Broncos were trying to run down the clock on their ensuing possession when linebacker Korey Toomer ripped the ball out of Jamal Charles' grasp, and Los Angeles recovered at the Denver 38. On the next play, Rivers connected with a streaking Travis Benjamin, who got behind safety Darian Stewart, for the touchdown with 7:00 remaining.

Earlier, Denver had extended its lead to 21-7 with a possession that began with an interception of Rivers by cornerback Bradley Roby, whose first-quarter pass-interference penalty figured prominently in a Los Angeles touchdown.

Siemian quickly moved the Broncos 43 yards downfield capped by his second scoring pass to Fowler, a 6-yarder with 10:27 left in the third quarter.

Denver had a first-and-goal at the Chargers 1-yard line but settled for a 20-yard field goal by Brandon McManus on the final play of the third quarter after Los Angeles' defense stuffed two runs and forced a third-down incompletion.

The Broncos led 14-7 at the half, snapping a tie behind Siemian's bootleg play for a 1-yard touchdown run with 5:27 left in the second quarter.

Finding no one open as he rolled out, Siemian tucked the ball away and faked his way past defensive end Joey Bosa en route to the score. Rookie Isaiah McKenzie jump-started the touchdown drive by returning a punt 31 yards to near midfield.

The Broncos' initial scoring drive was kept alive by a dropped interception by Chargers cornerback Casey Hayward. Siemian finished off the march with a 5-yard touchdown pass to Fowler, who made a diving grab and then took a choreographed bow with teammates in celebration.

Rivers led the Chargers on a 75-yard march ending in an 11-yard touchdown pass to running back Melvin Gordon. The Chargers got most of their yardage during the drive on a 40-yard pass-interference penalty called against Roby for grabbing at the jersey of Keenan Allen.

NOTES: The Broncos were without DEs Zach Kerr (knee bruise) and Jared Crick (back spasms), who were listed among the team's inactive players. RB Devontae Booker (wrist fracture) and QB Paxton Lynch (shoulder sprain) joined them on the sideline. ... The Chargers were without their top draft pick, WR Mike Williams, who was deactivated after missing practice in the week leading up to the opener due to a lower back injury that also kept him out of most of training camp. ... WR Geremy Davis was signed to the Chargers' roster during the weekend after the team waived CB Jeff Richards. ... Denver added NT Tyrique Jarrett to the roster after releasing NT Kyle Peko. ... The Broncos lost RG Ron Leary to a concussion in the third quarter. ... Rookie Chargers S Rayshawn Jenkins also sustained a concussion in the third quarter and missed the rest of the game.