The 2023 NFL season is up and running with some thrilling contests taking place across the nation over the weekend.

Here's a look at five things we have learned from Week 1 so far, with the Buffalo Bills at the New York Jets still to come on Monday night to complete the opening week of games.

Champions stunned on opening night

The first game of the season does have the tendency to surprise at times and the Detroit Lions' 21-20 win over the Kansas City Chiefs certainly did that and then some.

Kansas City, fresh off their NFL Championship success last season, were expected to run out comfortable winners in this one but quickly found themselves in an arm wrestle at Arrowhead Stadium.

The Lions went 8-2 in the last 10 games of the 2022/23 season and they stayed at that level in Week 1.

Detroit's brand-new backfield of David Montgomery and Jahmyr Gibbs combined for 28 carries, 118 yards and a touchdown, quarterback Jared Goff threw a touchdown to Amon-Ra St. Brown, and defensive back Brian Branch intercepted a pass tipped by Chiefs receiver Kadarius Toney and returned it 50 yards for six.

Perhaps the defeat will be a timely reminder for the Chiefs that the chasing pack is coming for them this year.

With a target on their backs, the Chiefs are still the +700 favorites to win the NFL Championship this season.

Rusty Eagles get the job done

After the heartbreak of losing the NFL Championship to the Kansas City Chiefs last season, the Philadelphia Eagles could have been forgiven for having somewhat of a hangover going into the new campaign, especially having not played their offensive starters at all in the preseason.

A trip to the New England Patriots was certainly a winnable game for the Eagles but, on the other hand, a potential banana skin if Nick Sirianni's side did not get things right against legendary Pats coach Bill Belichick.

Philly showed no signs of a hangover in the first quarter, as they raced into a 16-point lead at Gillette Stadium but the Pats responded with 14 of their own before half-time.

The game turned into a scrappy affair after that but the Eagles managed to grind out a 25-20 win in the end.

Kicker Jake Elliott made four field goals, quarterback Jalen Hurts linked with wide receiver DeVonta Smith for a score, and cornerback Darius Slay returned an interception 70 yards for a touchdown.

There's plenty of football to be played and it's understandable there would be rustiness from both teams going into this one.

Philly accomplished the most important thing, which was getting a win to open the season. The Eagles are now +750 to win the NFL Championship this season.

49ers impress against Steelers

The San Francisco 49ers are among the favorites for the championship this year (+800) and their Week 1 win over the Pittsburgh Steelers by a 30-7 score backed up the claims.

Quarterback Brock Purdy has plenty of pressure on his shoulders this season and he stepped up to the challenge as he tossed two touchdowns to wideout Brandon Aiyuk.

As for the Steelers, a disappointing defensive display will be early cause for concern and it's back to the drawing board for their next game at home to the Cleveland Browns in Week 2.

Steelers quarterback Kenny Pickett threw for 232 yards with one touchdown, but two of his passes were intercepted.

Pittsburgh couldn't get momentum on the ground, either: Najee Harris ran for 31 yards on just six carries.

Love shines in Chicago

Green Bay Packers began life without veteran quarterback Aaron Rodgers with an impressive 38-20 victory over the Chicago Bears at Soldier Field.

Quarterback Jordan Love has big shoes to fill following Rodgers' move to the New York Jets but he performed well in Chicago as the Packers made a flying start to the season.

He threw for 245 yards and three touchdowns in the season opener.

The Packers claimed the win and the bragging rights at Soldier Field and will be interesting to see how they get on this season.

Green Bay are available at +4000 to win the NFL Championship this season and +260 to win the NFC North.

A night to forget for the Giants

There will have been more than a few disgruntled Giants fans leaving MetLife Stadium on Sunday night as New York suffered an embarrassing 40-0 defeat to NFC East rivals the Dallas Cowboys.

Dallas' defense proved too much for the Giants, with the Cowboys recording seven sacks and two turnovers during the game.

The Cowboys' defensive performance was so overwhelming that quarterback Dak Prescott did not throw a touchdown pass in the blowout victory.

Running back Tony Pollard ran for two scores and KaVontae Turpin ran for one. DaRon Bland returned an interception 22 yards for six, and kicker Brandon Aubrey made both of his two field goal attempts.

The Giants were left shell shocked after the final whistle and some tough questions will have to be answered ahead of their road game at the Arizona Cardinals this weekend.

As for Dallas, it was a tremendous start to the season and they're now +1100 to win the NFL Championship this season.

The Cowboys are also available at +140 to win a competitive NFC East title, with the Eagles at -120 and the Washington Commanders at +1200.

New York are +1400 to turn things around and finish top of the pile in the division.