Chelsea shook up the Premier League on Sunday, beating London rivals Arsenal 1-0 at the Emirates Stadium to seriously damage their challenge for the title.
Per Mertesacker's sending off after 18 minutes handed the champions a crucial advantage in the first half, and Guus Hiddink's team capitalised five minutes later as Diego Costa struck.
Arsenal pushed hard in the latter stages of the match as they chased a result, even sending keeper Petr Cech forward for the final corner of the game, but the Blues remained calm and resolute to attain the victory—leaving Leicester City three points clear at the top.
Mesut Ozil returned to the Gunners starting XI after missing the previous match with a knock, and there was a place on the bench for Alexis Sanchez after a period out with injury.
Eden Hazard was named as a substitute after recovering from a recent groin strain, and Oscar stepped into Hiddink's team for Pedro.
It was hard work for Arsenal from the opening whistle, with Chelsea raising their game after months of inconsistency.
The flashpoint of the match proved telling across the 90 minutes, as Mertesacker clipped Costa as he ran through on goal, prompting referee Mark Clattenburg to immediately brandish a red card. The Spaniard had outsprinted the German international, and his lunging tackle allowed the Chelsea man to theatrically hit the floor.
Sky Sports Statto shared Mertesacker's reaction on social media:
Per Mertesacker's red card is the 12th in 48 PL games between the sides. It's the German's 2nd red card for Arsenal pic.twitter.com/ivQy4ECYO1— Sky Sports Statto (@SkySportsStatto) January 24, 2016
Golfer and Gunners fan Ian Poulter had no issues with the decision, but the incident prompted pessimism:
I have no problem with the red card. It had to be. last man... But Costa I can't stand. Chelsea will probably win 7 - 0 today.— Ian Poulter (@IanJamesPoulter) January 24, 2016
Chelsea quickly exploited their advantage in numbers as Arsenal manager Arsene Wenger reorganised, replacing Olivier Giroud with Gabriel Paulista.
The champions wrestled the lead after 23 minutes, as Costa latched on to a dangerous cross from Branislav Ivanovic. The Spain international made no mistake, slotting the ball past Cech.
Journalist and Arsenal supporter Piers Morgan was not enjoying his afternoon:
Chelsea continued to dominate through to half-time, with Ivanovic having a headed effort cleared off the line shortly before the break.
Wenger's side looked broken as they walked off the field, shell-shocked by the events of the opening 45 minutes. OptaJoe pointed toward the Gunners' disciplinary record against Chelsea:
7 - Arsenal have now been shown more red cards against Chelsea than they have any other Premier League opponent (7). Reckless.— OptaJoe (@OptaJoe) January 24, 2016
WhoScored.com shared statistics from the first half displaying Chelsea's advantage and highlighted the contribution of former Arsenal ace Cesc Fabregas:
Arsenal attempted to take control of territory in the second half, but the Blues looked motivated to hang on to their lead and remain in charge.
Chelsea was cool and calm in possession, and Wenger responded three minutes before the hour mark by unleashing Sanchez from the bench.
The hosts' lack of goals against the Stamford Bridge outfit was noted by AFP's Tom Williams:
Now nine hours since Arsenal scored a league goal against Chelsea.— Tom Williams (@tomwfootball) January 24, 2016
Wenger's men could not get to grips with the task at hand, and their problems further increased when Hazard's quality entered the fray for the final 13 minutes of the encounter.
The Gunners pushed hard in the final stretch of the game as Chelsea sat back on their heels, but Arsenal failed to create clear-cut chances despite their best efforts.
The hosts laid siege to the visitors' goal in the closing stages, desperately trying to force an equaliser, squeezing Chelsea into their penalty area. Sanchez went close as the ball pinged around the box, but Arsenal could not grab the goal they needed.
The atmosphere was charged as the Gunners pounded the Chelsea defence in stoppage time, but Wenger looked frustrated as the Blues defended in numbers to take the 1-0 victory.
Wenger was disappointed his team failed to earn a draw after a hectic end to the match, but added he believed Costa made sure Mertesacker saw red, per the Associated Press' Rob Harris:
Wenger on Diego Costa: "He got Mertesacker sent off"— Rob Harris (@RobHarris) January 24, 2016
The Arsenal boss also commented on his decision to replace Giroud after the sending off, per freelance writer Ben Dinnery:
Wenger on replacing Giroud: "We had long distances to go from our half (to CFC). Our chance was to have pace on the counter attack." #AFC— Ben Dinnery (@BenDinnery) January 24, 2016
Arsenal are back in Premier League action on Tuesday, Feb. 2, when they host Southampton. Chelsea feature on the following day, away at Watford.