In Everton's last five halves of football against top four competition, the club has given up one goal.
We can (and will) talk about multiple other developments for Roberto Martinez's side, but easily the most important development from the Toffees' last four matches in all competitions is the team's improved defensive performance.
The return of captain Phil Jagielka has surely helped the team, but a general focus on playing a safer game from front to back has played an even larger role.
Let's take a look at Everton's starting lineup to begin more closely examining the team's defensive improvement.
With Seamus Coleman injured, John Stones slid over to right-back and Ramiro Funes Mori kept his spot in the starting lineup. Leon Osman got a surprise start at left midfield, and Muhamed Besic kept his place in the center of midfield.
The Bosnian is at the heart of Everton's new-found defensive shape. Besic covered tons of ground, was a defensive force, and, perhaps most encouragingly, passed the ball with consistent accuracy. All of this is reflected in Besic's activity map, courtesy of FourFourTwo.com.
Besic had two created chances, five tackles, four clearances, two successful take-ons, and only six misplaced passes. There is little doubt that Besic is the best out-and-out defender among the team's options at central midfield, but I've expressed concern about his ability to help his team keep possession.
If he can continue to pass the way that he did against Manchester City, any such concerns will prove to be unfounded.
Gareth Barry had a characteristically strong performance in the center of midfield as well.
Barry's passing was equally impressive, while he also had four clearances, two blocked shots, and two tackles.
The passing tendencies of Besic and Barry reveal much of what worked for Everton in the first half. Both players made only a few passes forward, instead focusing on keeping the ball when they got it.
Against a side with as much quality as Manchester City, possessing the ball was always going to be key to Everton's success. By keeping the ball, often in the middle third without much attacking thrust, the Toffees assured that the likes of Sergio Aguero and Kevin de Bruyne wouldn't have the ability to do any damage.
As a result, possession in the first half was essentially an even split, though much more of the match took place in Everton's defensive third, as this graphic from EvertonFC.com indicates.
Everton actually slightly outpossessed City in the first half, while more than half of the half took place in the middle third. Of course, only 16 percent of the half occurred in Everton's attacking third, but the Toffees did still create chances, just on the counter attack.
Given how dangerous Romelu Lukaku and co. have been on the counter this season, an offensive plan with this focus was reasonable. Essentially then, Martinez's plan was to have his side possess the ball whenever possible, not forcing the issue and keeping the ball away from City. When City turned the ball over, the Toffees would spring a quick counter if available, but if not, keep the ball in the midfield in a composed manner.
This plan worked quite well for the opening 45 minutes, with Leon Osman nearly putting his side in the lead and Everton conceding a limited number of decent chances.
Once the second half began though, the Toffees' fortunes turned completely.
Manchester City figured out Everton's game-managing tactics, and started applying higher pressure in the midfield, limiting the Toffees ability to move the ball via short passes through the midfield. With the center of the field locked down, ideally Everton could have looked to the wings to add width and open up the pitch.
Everton's player influence map, courtesy of FourFourTwo.com, displays why attacking down the wings wasn't a reasonable option.
As usual, Gerard Deulofeu adopted a wide and advanced starting position, but with no Seamus Coleman in the lineup and heavy pressure in the center of midfield, getting the ball out to him was generally not a feasible goal.
On the left, Osman provided more width than Arouna Kone usually does, but he lacks the pace to play a traditional winger's role.
So, 25 minutes into the half, Martinez substituted the pair off the pitch, which was a reasonable move to make. What was not reasonable, however, was one of the changes he made. On came Steven Pienaar for Leon Osman, who is a true wide player, though he also lacked pace. But, with his ability to link up with Leighton Baines on the left, he certainly had a better chance of releasing the pressure than Osman.
On the right though, Martinez brought Kone in for Deulofeu, which made absolutely no sense. The Ivorian striker lacked the pace to be a danger on the counter, the defensive ability to help out with the dangerous Raheem Sterling, the playmaking ability to work the ball through the midfield, or even the general tactical awareness to stretch the field by providing width.
Without an outlet, Everton could not consistently get out of its own defensive third, inviting pressure and failing to create chances.
In all though, the day was successful. The Toffees managed to stay out of trouble and create some chances in the first half, then held on for dear life in the final 45 minutes. If the side's defense and midfield can continue to limit the opposition's chances as they have done in recent weeks, there is no reason why Everton cannot improve its league form and continue its exciting cup run.