As Marcel Halstenberg cut inside and curled home RB Leipzig's opening goal against Union Berlin on Sunday, you could tell this team meant business.

The flowing attack started on Leipzig's right-hand touchline with Lukas Klostermann driving forward and feeding Marcel Sabitzer at the top of the box. Union's defense were desperately backtracking, occupied by the diverting runs of Timo Werner and Yussuf Poulsen.

A rampaging Halstenberg sprinted up from left-back, collected possession from Sabitzer as the playmaker exploited the space opening up in front of him, and finished with aplomb.

It was a simple goal, but one that highlighted how RB Leipzig plan to tackle this season – attacking football characterized by lengthy spells of possession, intelligent movement, and pushing numbers forward.

Three more goals followed in a near-perfect display and announced the beginning of a new era under coach Julian Nagelsmann and Leipzig's emergence as a title contender.

The 32-year-old stands as one of the most promising young coaches in the world, but he now has a platform that can turn that promise into substance. At RB Leipzig, he has the required tools to mount a serious title challenge against favorites Bayern Munich and Borussia Dortmund this season.

Building on strong foundations

Nagelsmann has arrived at a club with solid foundations and has been given a headstart thanks to predecessors Ralph Hasenhüttl and Ralf Rangnick's groundwork over the past four seasons.

RB Leipzig's defense was the envy of the league under Rangnick last season, conceding just 29 goals. Under Nagelsmann, however, the team has already shown signs of improvement.

Too often last season, the Red Bulls found themselves undone by a disjointed attack lacking creativity and ideas. RB Leipzig fired nine blanks in the Bundesliga, four of them goalless draws against opposition in the bottom six.

Too much of the attacking load was placed on the shoulders of Werner (16) and Poulsen (15), who scored almost 50 percent of RB's Bundesliga goals in 2018-19.

In contrast, Bayern's top goalscorers Robert Lewandowski and Serge Gnabry (32 combined) accounted for just 36 percent of the Bavarians' goals. Paco Alcacer and Marco Reus (35) netted 43 percent of Borussia Dortmund's total tally.

With Nagelsmann's reputation so far built on a successful spell at Hoffenheim, where his team played an exciting brand of attacking football, the new coach highlighted the front third as an area for improvement in preseason.

Two particular demands? More possession and more goals from his midfield players.

Sabitzer driving Bulls forward

With captain Willi Orban marshalling a strong defensive line, Nagelsmann has little need to work on an already commanding defense. A three-man backline of Orban, the imposing Ibrahima Konate, and Nordi Mukiele (with Dayot Upamecano out injured) dominated the match against Union and snuffed out almost every attack before they could trouble goalkeeper Peter Gulacsi.

Up front, Nagelsmann knows he can rely on Werner and Poulsen to grab double-figure goals and so now he's looking to his midfield for improvement. Key to that development will be Marcel Sabitzer, who has stepped it up a level.

Three assists and one goal against Union Berlin, together with two goals against VfL Osnabrück in the German Cup, are ample evidence that the Austrian is purring at the start of this new season.

"I said in preseason that the midfield needed to be more dangerous, which perhaps Sabi took to heart," Nagelsmann said post-match on Sunday.

Sabitzer was everywhere, working hard from his right-wing role, involved in every Leipzig attack and harrassing an overwhelmed Union midfield and defense. An unsatisfactory goal-scoring record of just seven strikes in his previous 52 Bundesliga matches already appears to no longer be a problem.

"I like the way the coach let's us play and I wanted to pay him back. It has worked well for us twice now, which is great. Last season I struggled a bit in front of goal, but not anymore. I've worked hard in training and now it's paying off."

After criticizing RB Leipzig's transfer policy of signing youth instead of experience in preseason, Sabitzer looks like he's decided to fill the void of seasoned professionals himself.

Title challenge on

"We were able to react well in certain situations. We wanted to be variable – including when we had possession. We had a good mix of possession and phases of counter-pressing," Nagelsmann told the Bundesliga website post-match.

"If we replicate this performance against a few more opponents, then we have a chance to compete at the top," he continued.

Combined with RB Leipzig's strong starting XI, Nagelsmann had the luxury of bringing Emil Fosberg, Christopher Nkunku, and Konrad Laimer off the bench, while along with Upamecano, Jean-Kevin Augustin and Hannes Wolf are still to return from injury. Such depth bodes well for a season in which Leipzig will also be aiming to compete in the Champions League and German Cup.

The only cloud hovering over Nagelsmann's bright beginning is the future of Werner, with the striker's contract ending next summer. The club has said repeatedly that they won't accept losing him for nothing and sporting director Markus Krösche said a decision would be made in the next few days.

If Nagelsmann holds onto Werner, however, the chances of a sustained title challenge remain strong. A sterner test awaits RB Leipzig at home against Eintracht Frankfurt next Sunday, but based on their start under Nagelsmann they certainly have the goods to turn this Bundesliga season into a three-horse race.