Barcelona fielded its strongest side away to Roma, as did Real Madrid at home to Shakhtar Donetsk, Paris Saint-Germain hosting Malmo, Atletico Madrid away to Galatasaray, Bayern Munich away to Olympiakos and Juventus at Manchester City. None of them lost; in fact, all the European powerhouses won except Barcelona, which drew in the Italian capital — hardly a poor result.

So why did Arsene Wenger feel he had to make six changes when Arsenal traveled to Dinamo Zagreb? Arsenal was deservedly beaten 2-1 by a side that had failed to win in 15 previous appearances at this stage of the Champions League.

The Frenchman denied it, but it is difficult not to believe he had one eye on Saturday’s Premier League game against Chelsea and was confident his mix-and-match team could overcome opponents perceived to be among Europe’s weakest links in UEFA’s premier club competition.

True, Jose Mourinho selected a similar side against Maccabi Tel Aviv, but the Israelis were so inept Chelsea’s youth team would probably have won the tie.

The cream of Europe’s coaches chose their best XIs for this week’s Champions League games, yet Wenger begged to differ. His pointless tinkering and rotation cost Arsenal dearly in Croatia, and while the Gunners and Bayern Munich remain favorites to advance from the group, the loss gives them less room for future error in the remaining five games, two of which are against Bayern.

Wenger would argue that the six replacements were all full internationals who should not weaken the side. Most of Europe’s elite have squads bursting with internationals, but some are better than others and to change half your team disrupts the cohesion and rhythm, which was so obvious against Dinamo.

It will be business as usual on Saturday because Wenger and Mourinho will field their strongest sides at Stamford Bridge as two managers whose only common thread is their opinion of each other go head to head. Wenger secured his first win over the Portuguese in the Community Shield, but in the league Chelsea is unbeaten against Arsenal in their last seven encounters. The Gunners have failed to score in their last four league matches against the Blues, though Chelsea’s domestic form this season has seen it drop to 17th.

Incredibly and inexplicably, every Chelsea outfield player has lost form at once. In May, the Blues were champions, now they are unrecognizable from the side that dominated last season.

There are rumors and reports, inevitably denied, that the players no longer have total belief in the Special One, not least his crass handling of Dr. Eva Caneiro, who was a popular and respected figure with the squad. John Terry is no longer a permanent fixture, Diego Costa wants to fight the world, while Cesc Fabregas and Eden Hazard could hardly have started the season worse.

The pressure is mounting on Mourinho as Chelsea’s chances of retaining its title have already realistically disappeared. Losing is new territory for him and he needs to somehow rekindle Chelsea’s magic quickly. From Mourinho’s perspective, there is no better manager to do this against than Wenger.

Mr. Consistent: Gareth Barry will on Saturday make his 563rd Premier League appearance when Everton plays Swansea. As usual, he is unlikely to catch the eye or raise the pulse because the midfielder is a player who is taken for granted. He is an unsung hero who seems incapable of playing badly, a player always on the edge of the spotlight, but who is the glue that holds a side together.

The almost-famous Barry is fourth in the all-time Premier League appearance list, which is headed by Ryan Giggs (632).

Second is Frank Lampard (609) and third is David James (572). It is inevitable that Barry, 34, will overtake James in the coming weeks, while Lampard’s total is within his reach next season.

To take the record from Giggs would mean Barry playing 30-plus Premier League games — to feature in all 38 is unrealistic — this season, next season and the first third of 2017/18, when he would be 36. Not an impossible feat though logic suggests Giggs’ crown is safe and being second to the Manchester United legend is no disgrace.

While Giggs and Lampard are household names respected by all, Gaz Baz, as he is known, is permanently underrated by the public, but certainly not by his managers. True, he is one-paced and his speciality is unseen work which hardly makes him exciting to watch. He is in the history books as the first player to be cautioned 100 times in the Premier League, but Barry could never be classed as a dirty player.

He is happy to sacrifice personal glory for the good of the team and if he retires second to Giggs on the appearance list it would be just reward for his incredible consistency since making his debut for Aston Villa in May 1998.

Since 1998-99, only once has Barry played fewer than 30 league games. He has rarely been dropped during his career and has escaped any serious injury that virtually every player sustains at some point.

Initially a center-back or left-back, Barry became a defensive midfielder, the water carrier doing the work that provides the base for attackers to shine.

He made 365 league appearances for Villa before joining Manchester City in 2009. Barry helped City win the F.A. Cup and Premier League title during his five years with the club, and goalkeeper Joe Hart said: “Gareth is the man. When you start to panic, look at Gareth and he just keeps on doing what he is doing — and doing the unselfish role he does.”

Barry spent a season on loan with Everton before making the move permanent in July 2014, signing a three-year contract. Everton manager Roberto Martinez has no doubts about the influence of Barry and said: “On the pitch, you don’t get a better influence than someone like Gareth Barry, because he’s always in the middle of everything.

“He’s someone with composure and is an example. In terms of leadership, he is a very specific model. He leads with actions. He’s got incredible standards. Everything he does, he means it.

“Gareth’s not vocal just for the sake of it, but he will be vocal if someone drops their standard and lets their level drop below what we expect. For me, the best way to show leadership is to put yourself through actions and letting everybody else copy your example.

“Gareth has been an influential figure since the day he arrived, but with the maturity and experience he has at the club he has become an even more senior figure.”

Barry, who won 53 England caps between 2000 and 2012, will no doubt again be largely anonymous but hugely influential against Swansea as he edges closer to third on the Premier League all-time appearances table.

Make of this what you want: Signs outside Stamford Bridge warning against buying tickets from touts are in English and Japanese.

Christopher Davies was a longtime Premier League correspondent for the London Daily Telegraph.

Correction, Sept. 21, 2015:

Chelsea were incorrectly referred to by the nickname “The Gunners.” Chelsea’s nickname is “The Blues.”

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