The Atlanta Falcons saw their unbeaten start to the NFL season come to a shuddering halt Sunday with a 23-17 defeat to the Buffalo Bills on a day of upsets.

The Falcons, last season's beaten Super Bowl finalists, saw their perfect start derailed after a gritty performance by the Bills.

Falcons quarterback Matt Ryan threw for 242 yards from 24 of 42 attempts, but only connected for one touchdown.

Opposite number Tyrod Taylor finished with 182 yards, but it was good enough to see the Bills improve to 3-1 to lead the AFC East.

The key moment at Atlanta's Mercedes Benz Stadium came in the third quarter when Tre'Davious White galloped 52 yards for a touchdown following a Falcons fumble.

A Stephen Hauschka field goal put the Bills 17-10 ahead only for Ryan to connect with Justin Hardy with a three-yard pass to level the scores.

However two monster Hauschka field goals -- from 56 and 55 yards -- put the Bills up 23-17 and they held on to claim a deserved win.

"We knew coming into it that they had a very good defense," Falcons star Ryan said. "They have a lot of talent and we just made too many mistakes out there."

A good day for the Bills got better when AFC East rivals the New England Patriots suffered their second home defeat of the season as the Carolina Panthers closed out a thrilling 33-30 win at Gillette Stadium.

In the night game, the Seattle Seahawks took care of business by defeating the Indianapolis Colts 46-18.

Scotland-born Panthers kicker Graham Gano sealed a pulsating win for Carolina with a 48-yard field goal with just four seconds remaining.

Gano's winner was the final act of a dramatic fourth quarter which had seen Tom Brady lead the Patriots back from a 30-16 deficit to level at 30-30.

Brady, who finished with 307 passing yards including two touchdowns with no interceptions, looked to have rescued the reigning Super Bowl champions again after finding Dion Lewis and Danny Amendola in quick succession to tie.

- Newton decisive -

But Panthers quarterback Cam Newton led his team upfield with a decisive 10-play drive to engineer Gano's winning kick with no time left on the clock.

Newton finished with 316 passing yards for three touchdowns and also rushed for one score as the Panthers improved to 3-1 in the NFC South.

"I feel like this was a breakthrough game for us offensively," said Newton.

The Patriots meanwhile fell to 2-2 in the AFC East, with Brady left admitting the team were way off their peak.

"There's no guarantees and every year is different," said Brady. "We just haven't done a good job at home."

In Dallas, the Los Angeles Rams maintained their impressive start to the season with a 35-30 upset over the Cowboys at the AT&T Stadium.

Rams quarterback Jared Goff finished with 255 passing yards and two touchdowns, while the defense sacked Cowboys quarterback Dak Prescott three times to help set up the win.

Rams running back Todd Gurley meanwhile outshone Cowboys counterpart Ezekiel Elliott, finishing with 121 rushing yards and a further 94 receiving yards.

The Rams, under the guidance of Sean McVay, the youngest head coach in the NFL at just 31, now lead the NFC West with a 3-1 record.

Elsewhere Sunday, Houston Texans rookie quarterback Deshaun Watson had another scintillating performance in a 57-14 thrashing of the Tennessee Titans.

Watson threw for four touchdowns, finishing with 283 yards after making 25 completions from 34 attempts.

In the early game in London, Drew Brees passed for 268 yards and two touchdowns to lead the New Orleans Saints to a 20-0 win over a lackluster Miami Dolphins side.

The win saw the Saints improve to 2-2 after an 0-2 start to the season.

"Those first two weeks weren't what we aspired to be -- we played two really good football teams," Brees said.

Since then, "we've had two road wins at Carolina and here against the Dolphins, who have a really good defense and are a really good football team."