Arsène Wenger marked the 18th anniversary of the start of his Arsenal reign with an emphatic 4-1 win over Galatasaray on Wednesday. But it is Sunday’s trip to Stamford Bridge to take on Chelsea that will be a much truer test of whether he is capable of replicating the success enjoyed during the first nine years of his stay rather than the frustration of the subsequent nine.

No club has symbolized Arsenal’s fall from the title-winning swagger of Wenger’s early years than Chelsea. Within a year, Roman Abramovich’s money and José Mourinho’s acumen had dethroned Arsenal as champions of England. In total, Chelsea have won 11 trophies since Arsenal last hoisted the Premier League trophy aloft. Perhaps most gallingly, Chelsea became the first London club to win the Champions League, despite Arsenal having qualified for the competition for 17 consecutive seasons.

It is not just the trophy count that has marked the dramatic shift in power in England’s capital. The clubs’ head-to-head contests have regularly crudely exposed what was missing from Arsenal’s repertoire. Didier Drogba scored 13 goals in 14 matches during his first spell at Chelsea, with Arsenal consistently unable to cope with the striker’s physical approach.

Meanwhile, it speaks volumes that Mourinho has never come out on the losing side against Wenger. The last time the two sides met at Stamford Bridge showed exactly why. Chelsea were 3-0 up by halftime and by the end of 90 minutes it was 6-0. Mourinho, the arch-pragmatist, had once again devised a brilliant game plan to exploit the opposition’s weaknesses, while Wenger, the arch-idealist, stood by as his side were torn apart in a match that marked his 1,000th in charge and was one of the most astounding games in recent memory.

When the teams walk out at the same venue on Sunday, we are likely to quickly find out whether Wenger has learned his lessons and mediated his laissez-faire approach to tactics. The win over Galatasaray showed off the investments made in enhancing Arsenal’s attacking ability in the past two summers. Alexis Sanchez and Mesut Ozil provided examples of the world-class talent that, after years of prudence in the transfer market, Arsenal paid big to secure, while Danny Welbeck’s pace in behind that garnered him a hat-trick illustrated why it was so important for Wenger to add to his forward options late in the transfer window.

While there have been obvious upgrades, Arsenal’s major problem in recent years has never been going forward. Against teams that allow them space to play, like Galatasaray, Arsenal have generally been a joy to watch. It is when they are put under pressure that it has all gone wrong in recent times. Last season, they lost every road game at Chelsea, Liverpool, Manchester City and Manchester United, by a total scoreline of 20-4.

A key factor in all four of those defeats was the gaping hole regularly witnessed in front of Arsenal’s defense. It meant that as soon as possession was turned over, as it is all too often when they are pressured, the opposition have a clear run at Arsenal’s back four, which is generally a back two with the full-backs caught way upfield. Chelsea spotted this weakness better than any team, with Mourinho setting his side loose upon Arsenal from the first whistle.

They could well fancy their chances of doing so again on Sunday. Wenger again failed to sign a natural defensive midfielder in the summer or even a midfielder to add some physicality. Instead, he has tried to shore up his midfield by opting for a 4-1-4-1 formation and sacrificing Ozil by shunting him to the left. But with Mikel Arteta and Aaron Ramsey ruled out as part of yet another injury crisis, Wenger will be prevented from going with that system, at least not with the players for which it was intended.

Mathieu Flamini will be charged with protecting Arsenal’s defense at Stamford Bridge, but, while he is the closest thing to a natural holding midfielder in their squad, the Frenchman has had a poor start to the campaign. Having failed to track back for Manchester City’s opening goal in a 2-2 draw three weeks ago, he gave up possession to allow Tottenham to take the lead last weekend. Mourinho will doubtless have had a wide grin spread across his face seeing the way Flamini succumbed to Spurs’ pressure.

While Arsenal have not addressed their weaknesses, Chelsea and Mourinho have demonstrably taken care of theirs. Gallingly for Arsenal fans, former Gunners captain Cesc Fabregas has added an extra creative spark, while Diego Costa has provided the lethal efficiency in front of goal that was so lacking last season. Despite starting in last week’s 3-0 win over Aston Villa and doing so again in the midweek Champions League triumph at Sporting Lisbon, Mourinho confirmed that Costa would be in the lineup against Arsenal. The Brazil-born Spain international has been hampered by a hamstring injury in recent weeks that prevented him from playing two games in quick succession.

The changes made over the summer have undoubtedly made Chelsea more of an offensive threat in an effort to prevent the same bluntness that cost them the Premier League title last season. Yet, with Fabregas introduced to the midfield, Chelsea have yet to convince that they have got the balance right in order to maintain the same defensive solidity. A 6-3 win over Everton and 4-2 victory over Swansea were most un-Mourinho-like, as was conceding a late equalizer to Manchester City. Back-to-back clean sheets for the first time this season suggests an improvement, although there remains work to be done. Not nearly as much work, though, as there is for their next opponents. And unless Wenger is prepared to adopt just a hint of his counterpart’s pragmatism then it could be yet another 90 minutes that exposes that Arsenal remain some way short of ending their title drought.

Prediction: Chelsea 3-1 Arsenal

Injury news

Drogba and Ramires are Chelsea’s only absentees, with the pair expected to return after next week’s international break.

Arsenal: As well as Arteta and Ramsey, Arsenal remain without long-term absentees Olivier Giroud and Mathieu Debuchy. Theo Walcott and Serge Gnabry are set to return to full training next week. Nacho Monreal could return to the squad on Sunday after a back injury.

Kickoff time: 9.05 a.m. EDT

TV channel: NBCSN

Live stream: NBC Sports Live Extra