Rookie Koo could have sent last weekend’s match at Denver into overtime had he not seen a retaken 44-yard kick blocked by Shelby Harris.
The South Korean-born kicker found himself in the same position this week with five seconds left on the clock in the fourth quarter, but put his effort from an identical distance wide and the Dolphins held on.
By contrast, Miami kicker Cody Parkey converted four field goals - the last one from 54 yards with just over one minute remaining.
In a notoriously insecure job, Chargers coach Anthony Lynn didn’t exactly give Koo a vote of confidence afterwards.
“We’re always looking to improve,” Lynn said when asked about Koo’s prospects.
Elsewhere, the Atlanta Falcons built a big lead over the Green Bay Packers, then watched it being chipped away.
But, unlike in the Super Bowl against the New England Patriots last season, Dan Quinn’s side held on for victory on Sunday night.
In the first regular season game at $1.5 billion Mercedes-Benz Stadium, the Falcons led by 24 points after three quarters and didn’t wilt after two early fourth-quarter touchdown passes by the Packers’ Aaron Rodgers in a 34-23 victory.
“It was a special night for our fans,” Quinn said. “Everyone was pumped, and we wanted to make sure we delivered.”
Falcons quarterback Matt Ryan completed 19 of 28 passes for 252 yards and a touchdown. Julio Jones had five catches for 108 yards, and Devonta Freeman rushed for 84 yards and two short touchdowns.
Atlanta safety Desmond Trufant, who missed the second half of last season, had a 15-yard fumble return for a touchdown and set up another TD with an interception.
“Those were the turning points,” said Quinn, whose team had a late defensive stand to beat the Chicago Bears in the opener. “Last game we had a stand-down at the end. This was a total team victory.”
Following a loss in their opening game, reigning Super Bowl champions the New England Patriots bounced back with a win against the New Orleans Saints.
An impressive display from Tom Brady, who threw three touchdown passes in the first quarter - a career first for the quarterback - helped the Patriots to a 36-20 victory.
The 40-year-old completed 30 out of 39 passes for 447 yards without an interception.
Meanwhile, the Denver Broncos’ Trevor Siemian equalled a career-best with four touchdown passes in a game that saw his side triumph 42-17 over the Dallas Cowboys.
The same could not be said for Cowboys running back Ezekiel Elliott, who managed a career-low eight yards from nine carries.
Despite signs of a fightback from Dallas in the second quarter, with Dez Bryant claiming a touchdown in the early stages, the Broncos went on to score two touchdowns in the third to set up the win.
After an hour-long lightning delay, Aqib Talib sealed victory when he intercepted Dak Prescott in the end zone and returned the ball 103 yards for a touchdown.
Elsewhere, the Oakland Raiders put in a dominant performance to beat the New York Jets 45-20 and make it two wins from the first two games for the first time in 15 years.
Marshawn Lynch starred in his debut home game with the Raiders, scoring a touchdown in the second quarter.
Rookie Kareem Hunt continued his stunning start to the season as he scored two touchdowns to help the Kansas City Chiefs to a 27-20 win in a tightly-fought contest with the Philadelphia Eagles, while the Pittsburgh Steelers triumphed 26-9 at home to the Minnesota Vikings.
The Chicago Bears were rolled over 29-7 by the Tampa Bay Buccaneers, while the Washington Redskins claimed a 27-20 victory over the Los Angeles Rams.
Little action was seen in the Carolina Panthers’ 9-3 win over the Buffalo Bills, while the Seattle Seahawks triumphed 12-9 against the San Francisco 49ers.