Is this Man City's best defence and does it suit Ruben Dias?

An hour and 15 minutes before events got underway at the Etihad Stadium, Pep Guardiola picked a starting XI that did not lead to raised eyebrows and mass consternation.

No midfield diamond, like the one that quickly lost its shine in a 3-0 defeat to Liverpool at Anfield in 2018; no overt caution as in the 1-0 loss at Tottenham that preceded a crazy second leg and an exit on away goals; no unwieldy 5-3-2 within which City froze so badly against Lyon last year.

Much of the runaway Premier League leaders' success this season has been based upon Guardiola harnessing the full depths of a talent-rich squad, mastering the art of pandemic football through shrewd rotation. So, given his line-ups have become increasingly tricky to predict, the prospects of a pre-match bolt from the blue were reduced.

However, if he has a best XI, the side that eventually prevailed 2-1 against Dortmund were something close to it. A midfield trio anchored by Rodri, ablaze with Kevin De Bruyne's creativity and gilded by Ilkay Gundogan's supreme movement and timely goals. Up front there was, well… no one in particular as Riyad Mahrez and Phil Foden hovered around false nine Bernardo Silva.

And at the back, in front of an unusually erratic Ederson, were City's four best defenders this season. There was Joao Cancelo, the wildcard full-back/midfield hybrid who has given Guardiola's side a new dimension and added control. On the other flank, Kyle Walker – a right-back in the most conventional sense and one of Guardiola's most reliable performers of the past four campaigns.

At centre-back, the reborn John Stones was alongside Ruben Dias. An error on his England return last month stood out so much because Stones has been immense in sky blue this term. City have only conceded seven times with him on the field this season.

Then there is Dias, who joined as a club-record signing from Benfica in the aftermath of a 5-2 defeat to Leicester City. Such humiliation has never looked like being repeated with the Portugal international in harness.

"He’s been so important so far but still we have two months before the end of the season," Guardiola said ahead of Saturday's match with Leeds United, against whom Dias made his debut six months ago.

"He has been so important in the leadership and quality he has."

Despite their impressive individual performances, the Dortmund game was only the fifth time the Walker-Stones-Dias-Cancelo quartet has lined up together.

Given City have two Wembley dates this month and possibly more showpiece encounters to come as they pursue honours on four fronts, their potential status as a go-to defensive line is interesting, mainly because it is a setup in which the influential Dias seems a little uncomfortable.

The reason for this is rooted in the fact that, since City embarked upon their remarkable ongoing run of 27 wins in 28 matches, Guardiola's back four has not really been a back four.

In possession, which is most of the time when you're Manchester City, Cancelo's role is generally to bolster the midfield numbers. When Guardiola highlighted some of City's struggles in central areas against Dortmund, it was Rodri and Cancelo – tellingly not one of the Spain international's teamsheet midfield colleagues – who he namechecked.

That leaves three strung across the backline to start the build-up, a fundamental basis for any strong Guardiola performance. When Cancelo has started nominally from right-back, that three is usually Stones-Dias-Oleksandr Zinchenko. Walker's starts at right-back have often come with the left-footed central defender Aymeric Laporte in the line-up, meaning the back three in possession is Walker-Dias-Laporte.

Dias thrives in this position at the heart of things, with ball players on their natural sides flanking him. The problem when Walker and Cancelo start is Dias ends up on the left of the three, with Stones central.

"You are completely right, good point," Guardiola conceded when it was raised Dias was put slightly out of his comfort zone in midweek.

"We don't have left footer to pass the ball to the wider winger quicker with a natural left foot. That's true.

"But in that game we needed specifically Ruben in that position, with John, and that's why you use it. We won for other aspects in other positions and other situations."

So, Guardiola felt the trade-off was worth it due to benefits elsewhere. Considering how City came on strong down the stretch before Foden's dramatic winner, it is hard to argue too much.

A closer inspection of the games Walker, Stones, Dias and Cancelo have started shows Marco Reus' equaliser for Dortmund was the first goal City have conceded in this configuration. Previously, they drew 0-0 at Manchester United, beat Southampton 1-0 and Aston Villa and Borussia Monchengladbach 2-0, although Walker went off injured before half-time versus Villa and was replaced by Zinchenko.

But what of Dias? When starting with Stones, Walker and Cancelo, he averages 12 fewer passes per 90 minutes (78 down from 90) at a lower accuracy (91.1 from 93.8) than his overall season statistics, suggesting he is not so sure in possession on his unfavoured side of the field.

His duel success rate drops from 62.7 per cent to 50, with aerials falling from 66.1 to 54.5 per cent. His tackles per 90 minutes track upwards slightly from 0.9 to 1.3, although this could indicate the build-up flaws of this back three/four means more last-ditch defensive work.

Another game where Dias was on the left of the three in possession came in February against West Ham, where Walker started and Zinchenko performed the Cancelo role from the left.

Although Dias and Stones were the goalscoring heroes in a 2-1 win, City were ragged and Opta's expected goals (xG) figures for the game saw David Moyes' men 1.9-0.5 to the good at full-time, indicating Guardiola's normally smooth outfit rode their luck.

These are minor drop-offs and it is not as if City have looked useless in the games mentioned above. However, as Guardiola often likes to say, the biggest games can come down to the "small details".