Zero.

That's not only the amount of points Cologne have picked up this season, it's also the number of goals Borussia Dortmund have conceded.

Peter Bosz has done what no newly appointed Bundesliga coach has ever done before, leading his side to five clean sheets in his first five Bundesliga matches following Wednesday's 3-0 win against Hamburg. 

Dortmund sit atop the Bundesliga table as a result and is one of three unbeaten teams left after the first five matches. So how did they do it?

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No shot

Dortmund's opponents have barely had a shot at beating them. Literally.

On average, Dortmund's defense has allowed opposition teams just 6.8 shots per game, the best mark in the Bundesliga. Less than a quarter of those have been on target.

Part of the reason for those statistics is the possession BVB enjoy - Bosz's men have, on average, 64.3 percent of the ball, another Bundesliga best. But even when their opponents have possession, it's difficult to find a way through – opponents have dribbled past Dortmund players only 3.8 times per game, another league-leading stat.

That said, Dortmund have yet to face any of the best attacking teams in the league. All five of their opponents to date – Wolfsburg, Hertha Berlin, Freiburg, Cologne and Hamburg – are in the bottom half in the league in terms of goals scored, and, besides Cologne, are also in below the league average in shots per game.

What happened in London?

Tottenham Hotspur have been the only team to expose Dortmund's defense this season, but they did so in a big way. The London side used quick counter attacks and finished clinically to beat the Bundesliga leaders 3-1 in the Champions League.

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Aside from Spurs' attacking incision, Roman Bürki was a big reason for the blip. The goalkeeper allowed two near-post goals from tight angles that he should have saved. In addition to his errors, he wasn't helped by the fact that Dortmund's central defenders struggled to keep up with Tottenham's pacey forwards.

Omer Toprak was making his first start of the season after he replaced the injured Marc Bartra in the game against Freiburg the weekend before. He had played with long-time starter Sokratis Papastathopoulos in preseason, but had not played much with him since, explaining the pair's uncertainty. After that shaky start, the two have been dominant, part of the reason for Dortmund's success.

No captain, no problem

Dortmund's impressive defensive record has come despite the fact Marcel Schmelzer has missed most of the season due to injury. The skipper has only played in his side's draw in Freiburg and went off injured following a wild challenge by Yoric Ravet – one for which the Freiburg winger was sent off.

But Dan-Axel Zagadou, who Dortmund acquired from Paris Saint-Germain's youth academy, has made Schmelzer's absence more bearable. The French teenager has been dribbled past just once in five Bundesliga games, a remarkable feat for someone who has mostly played centrally. Jeremy Toljan also held his own against Tottenham in the Champions League, but Zagadou appears to be a Bosz favorite.

When will the first goal come?

As good as Dortmund's defense has been, they clearly won't go an entire Bundesliga season without conceding a goal. But it may be a while until they are finally breached.

Borussia Mönchengladbach, Dortmund's next opponent, have already been shut out by Eintracht Frankfurt this season. Augsburg, the opponent after that, have gone without a goal twice, against Magdeburg in the German Cup and Hamburg in the Bundesliga.

RB Leipzig, who travel to Dortmund in October, may be the team that finally breaks Dortmund's defense, but have been bipolar offensively. They put four past Freiburg in their first match of the season, but failed to find the back of the net against Augsburg in their game on Tuesday. But quick attackers like Timo Werner, Naby Keita and Jean-Kevin Augustin might expose the same weaknesses as Tottenham.

No matter when their shutout streak comes to an end, Dortmund appear to have a defense good enough to put them in real contention for their first league title in six seasons.