It's been a peculiar and somewhat unusual week for Chelsea -- two good performances in tricky contests against Barcelona and Manchester United, but little to show for their efforts. Having opened the scoring in both matches, Antonio Conte's men will feel disappointed not to be taking a first-leg lead to the Nou Camp, and underwhelmed at being defeated 2-1 at Old Trafford.

It's rare to be speaking about Chelsea in these terms, because this is a club that has spent much of the last 15 years doing the opposite -- winning without playing well. In an era where every club appears desperate to "play the right way", where everyone from Barcelona to West Ham seems to insist their club has a history of good attacking football, Chelsea have been largely resistant to this movement. Chelsea's modern era of success was effectively started by Jose Mourinho, a manager who cares solely about results, and little about quality of play, and the club has broadly played Mourinho-esque football ever since.

That can be explained, in part, by the composition of their sides. Chelsea haven't always boasted a genuine midfield playmaker, generally preferring strong, energetic and defensively reliable options instead, but have generally been strong at either end of the pitch. John Terry was one of the Premier League's most solid defenders for more than a decade, and while there have been some flops upfront -- Fernando Torres, Andriy Shevchenko -- the Roman Abramovich era has largely been spent with either Didier Drogba and then Diego Costa at striker. As other sides experimented with cuter, more technical players, Chelsea had no-nonsense strikers who put the ball in the net.

At the moment, Chelsea are in a very different situation. At either end of their 3-4-3 system -- excluding the goalkeeper -- they have their least experienced players, Andreas Christensen and Alvaro Morata. Their problems this week were essentially down to these two: Christensen made a crucial mistake to allow Barca back into the game at Stamford Bridge, while Morata looked out-of-sorts against Manchester United. Chelsea, for the first time in a while, are having to suffer while these players are still developing.

This, in itself, is another relatively new problem for Chelsea. Over the last 15 years Chelsea have almost always bought ready-made players, generally internationally proven footballers who are already at their peak. The club seemingly has no interest whatsoever in bringing through players from its hugely successful youth team, a long-standing problem.

They've also tended to loan out talented players bought from elsewhere rather than develop them in-house -- Thibaut Courtois was loaned out to Atletico for years, even when he was clearly better than Petr Cech, and Kevin De Bruyne was loaned and then sold to Wolfsburg. Chelsea will protest that De Bruyne wasn't happy sitting around on the bench, but that's not really the point -- other managers would have used a player of that potential in the first team immediately. If De Bruyne made some mistakes, and played inconsistently, that was just the price you had to pay.

Alvaro Morata and Andreas Christensen have each experienced their fair share of ups and downs this season at Chelsea. Photo by John Walton/PA Images via Getty Images)

But this simply isn't in Chelsea's thinking -- their policy was that, to be ready for a first-team place at Chelsea, a footballer needed to have 100 professional games under his belt. The number itself is relatively immaterial -- it could be 75, or 125, or 150. The point remains: Chelsea actively decided they wanted to opt out of that "development" stage, when players are prone to inconsistency.

Now, they're facing that problem. Christensen is a hugely talented defender: physically impressive, positionally disciplined and positive in possession. He's clearly now Chelsea's first choice as the spare man instead of David Luiz, and has largely enjoyed a fine campaign until now. The Premier League, though, is physically demanding: a 38-game season, no winter break, more lenient refereeing -- you've heard all the reasons before. Christensen enjoyed two good campaigns on loan at Borussia Monchengladbach, but changing country and league brings difficulties, and playing for the champions, who are also competing in the Champions League, brings added pressure.

Christensen has arguably been culpable for Chelsea's last three concessions. The wayward pass across his own box against Barcelona was clearly a mistake. For Romelu Lukaku's equaliser on Sunday, Christensen had been on the floor, and was only half-playing having taken a bang to the head. Perhaps he was legitimately hurt, but a more experienced centre-back might have put the pain aside for 20 seconds and ensured his side didn't concede. He was then caught under Lukaku's cross, allowing Jesse Lingard to steam in for a winner. Not a glaring error, but Chelsea's primary defender will always be asked questions when a player like Lingard heads home from point-blank range.

At the other end, Morata has been out of the side recently amongst on-pitch issues and off-field personal problems, but returned at Old Trafford and looked short of full sharpness. Morata is a relatively experienced player for his age, a multiple title winner, an international and a Champions League finalist with two different clubs. But the purchase of Morata to act as Chelsea's first-choice centre-forward felt very un-Chelsea like, as Morata is completely unaccustomed to being a regular starter. In his last three full seasons he played, respectively: 1,331 league minutes, 1,456 league minutes and 1,321 minutes. This season he has already played 1,641 league minutes at Chelsea.

A complete season in four of the top five leagues in Europe is 3,420 minutes. In other words, Morata had never played in more than half of his side's league campaign. Is it any wonder that, while Morata started excellently and clearly has enough talent for the league, he's struggling after Christmas? He passed his most-ever league minutes for a campaign on Jan. 13. He's having to find new energy reserves, experiencing a pressure he's never faced before.

Neither player should be written off: Morata is still averaging a league goal every 164 minutes while Christensen has been largely excellent aside from the last week. This time next year, they'll be in even better shape. But this is the reality of developing players: if you want the rainbow, you've got to put up with the rain. This week, where the games are won and lost -- the two penalty boxes -- Chelsea have come up short.