Jose Mourinho had several tough decisions to make ahead of Saturday's crucial match against Arsenal, including perhaps the toughest of all: which two of John Terry, Gary Cahill, and Kurt Zouma to pick to start in central defense. Regardless of whom he picked, he would've been criticized had we failed to win; that's the nature of the job.
There were pros and cons for all three. John Terry has had a rough start to the season, but he's hardly been alone in that regard and he remains the club captain (leader, legend) and in many respects, the heart and soul of the team. Gary Cahill has been his usual consistent self, more or less, but he's been slowed by the broken nose and the mask he's been required to wear. Kurt Zouma meanwhile, despite working on a four-match starting streak, is still just 20, still quite raw at times, and prone to the odd mistake or two.
The easiest decision of all would've been to go back to the tried and trusted Terry-Cahill pair, which worked so well last season. Mourinho was restoring other underperforming stars for this match after the midweek Champions League rotation, including Branislav Ivanovic and Nemanja Matic (both of whom repaid his trust quite handsomely), so it could've been very easy to bring Terry back in as well. It could've also quieted the nonsense rumors of a rift between manager and captain, which have been making the rounds over the past week, as a side benefit.
Instead, Mourinho opted for youth and speed over experience and veteran leadership.
"John Terry doesn't need me to speak with him because he knows what I feel and think. He knows he's my man. If I have to choose one of 25 to be my man he's the first. He knows I care about him as a player and a person. He knows my decision had only one intention, which was to help my team win the match. I thought Arsenal would come to play a defensive game, with a very fast striker who gets behind people. If we didn't need to win the game so much we probably would have kept our block lower and more compact, but because we desperately needed a victory we couldn't wait, we had to bring our defensive line up."
"Playing against Walcott, the best player we have is Zouma. John knows how I think and if he's normally a great captain, today he was even better. If every player had lots of respect for him, the way he's reacted in the last days to this situation, he has even more respect from the players. If you want to paint a dark picture, I ask you please don't because it's not the reality. He's in great condition and a great situation with the manager and club."
-Jose Mourinho; source: Chelsea FC
So, it was a combination of setting up to attack by playing a high line and expecting to face the countering speed of Walcott rather than the presence of Giroud up top. Mourinho's guess was proven correct when the lineups were announced; and the overall gambit proven correct when Cahill and Zouma not only marshaled an effective backline, but the latter also popped up to score the winning goal.
As far as Terry — who made sure to applaud and celebrate Zouma's goal with enthusiasm, no doubt expecting the TV cameras to find him just then — we'll just have to trust his and the manager's words that everyone can handle this paradigm shift without creating a sideshow. We saw Petr Cech do just that last season; there's little reason to think John Terry couldn't carry himself with the same dignity, dedication, and professionalism.